TJ 



:n 



ZAND'S SCIENCE $ERIE3. 



CO Cents* 

J T E A M 



;oiler Explosions. 

BY 

ZERAH COLBUEN. 

Htrttetr, tottf) an £ntrofciu< mr, fcu 
ROBERT iL THURSTON, 




NEW YORK 

D. VAN NOSTRAND COMPANY, 

23 Murray and 27 Warren Street. 

1890. 



THE VAN NOSTRAND SCIENCE SERIES. 

18mo, Green Boards. Price 50 Cents Each. 
JLmplu Illustrated when the Subject Demands. 

No. 1.— CHIMNEYS FOR FURNACES, FIREPLACES AND 
STEAM BOILERS. By R. Armstrong, C. E. fed 
Edition, with an Essay on High Chimneys, by 
Pinzger. 

No. 2— STEAM BOILER EXPLOSIONS. ByZerah Colburn. 
No. 3.— PRACTICAL DESIGNING OF RETAINING WALLS. 

By Arthur Jacob, A. B. 
No. 4.— PROPORTIONS OF PJNS USED IN BRIDGES 

By Charles Bender, C. E. 
No 5.— VENTILATION OF BUILDINGS. By W. F. Butle: 

Edited and Enlarged by Jas. L. Greenleaf. 

Edition. 
No. 6.— ON THE DESIGNING AND CONSTRUCTION OF 

STORAGE RESERVOIRS. By Arthur Jacob, A.B. 
No. 7.— SURCHARGED AN DJD EFFERENT FORMS OF RE- 






LIBRARY OF CONGRESS. 

Shelf -..^ 

UNITED STATES OF AMERICA. 



By 

itions 

ch is 

J ELS 
Wor- 

nthe 
rican 



f. W. 

J. J. 

ch is 
r Ed. 



No. 14.— FRICTION OF AIR IN MINES. By J. J. Atkinson. 

No. 15.— SKEW ARCHES. By Prof. E. W. Hyde, C. E. 

No. 16.— A GRAPHIC METHOD FOR SOLVING CERTAIN 

ALGEBRAICAL EQUATIONS. By Prof. Geo. L. 

Vose. 
No. 17.— WATER AND WATER SUPPLY. By Prof. W. H. 

Corfield, M. A. 
No. 18.-SEWERAGE AND SEWAGE UTILIZATION. By 

Prof. W. H. Corfield. 
No. 19.-STRENGTH OF BEAMS UNDER TRANSVERSE 

LOADS. By Prof. W. Allan. 
No. 20.— BRIDGE AND TUNNEL CENTRES. By John B. 

McMasters, C. E. 
No. 21.— SAFETY VALVES. By Richard H. Buel, C. E. 



■ 



VAN NOSTRAND SCIENCE SERIES. 



[GH MASONRY DAMS. By John B McMaster. 
HE FATIGUE OF METALS UNDER REPEATED 
STRAINS, with various Tables of Results of Ex- 
periments. From the German of Prof. Ludwig 
Spangenberg. With a Preface by S. H. Shreve 
PRACTICAL TREATISE ON THE TEETH OF 
WHEELS, with the Theory of the Use of Robin- 
son's Odontograph. By Prof. S. W. Robinson. 
HEORY AND CALCULATIONS OF CONTINU- 
OUS BRIDGES. By Mansfield Merriman, C. E. 
RACTICAL TREATISE ON THE PROPERTIES 
OF CONTINUOUS BRIDGES. By Charles Bender. 

0& BOILER INCRUSTATION AND CORROSION- 
By F. J.Rowan. 
-ON TRANSMISSION OF POWER BY WIRE 
ROPES. By Albert W. Stahl. 

MJECTORS ; THEIR THEORY AND USE. Trans- 
lated from the French of M. Leon Pouchet. 

TERRESTRIAL MAGNETISM AND THE MAGNET- 
ISM OF IRON SHIPS. By Prof. Fairman 
Rogers. 

THE SANITARY CONDITION OF DWELLING 
HOUSES IN TOWN AND COUNTRY. By George 
E. Waring, Jr. 

CABLE MAKING FOR SUSPENSION BRIDGES, 
as exemplified in the construction of the East 
River Bridge. By Wilhelm Hildenbrand, C. E. 

MECHANICS OF VENTILATION. By George W. 
Rafter, C. E. 

OUNDATIONS. By Prof. Jules Gaudard, C. E. 
Translated from the French. 
-THE ANEROID BAROMETER: Its Construction 
and Use. Compiled by Prof. G. W. Plympton. 
3d Edition 
MATTER AND MOTION. By J. Clerk Maxwell 
GEOGRAPHICAL SURVEYING: Its Uses, Methods 
and Results. By Frank De Yeaux Carpenter. 
AXIMUM STRESSES IN FRAMED BRIDGES. 
By Prof. Wm. Cain. 

HANDBOOK OF THE ELECTRO-MAGNETIC 
TELEGRAPH. By A. E. Loring, a Practical Tel- 
egrapher. 2d Edition. 
TRANSMISSION OF POWER BY COMPRESSED 
AIR. By Robert Zahner, M. E. 
TRENGTH OF MATERIALS. By William Kent. 
OUSSOIR ARCHES, applied to Stone Bridges, Tun 
nels, Culverts and Domes. By Prof . Wm. Cain. 
r AVE AND VORTEX MOTION. By Dr. Thomas 
Craig, of Johns Hopkins University . 



STEAM 

Boiler explosions. 

BY 

ZEKAH COLBUEK 

2Strttetr t tottj) an XnttoWction f *$ 
EOBEKT H. THUESTOK 




NEW YORK 

D. VAN NOSTRAND COMPAISTY, 

23 Murray and 27 Warren Street. 

1890. 




y* 









Copyright, 1890, 
D, Van Nostrand Co. 



Hf 



iV 



-i 



LC Control Number 



.0 




tmp96 027062 



INTRODUCTION. 



The following little treatise on the sub- 
ject of Steam-boiler Explosions is a 
" classic" in its department of engineer- 
ing literature. Its author, Zerah Col- 
bttrk, was one of the most remarkable 
and most talented men that the construc- 
tive profession has ever known. De- 
scended from a family noted for its intel- 
ligence, and especially for talent in math- 
ematics and the sciences, he fully sus- 
tained its reputation. For many years 
connected with that famous periodical the 
"London Engineer" he finally severed 
his connection with it, to found another 
now no less famous journal, "Engineer- 
ing" This he promptly made a success 
in all respects, and a success it remains 
to-day, in the hands of Messrs. Maw and 
Dredge, his hardly less talented and en- 

3 



terprising lieutenants. He broke down 
from over-work, after a time, and re- 
mained in a state of nerve-exhaustion for 
two years or more, able to do little or no 
work on his new journal, and sustained 
only by the life, energy, and ambition of 
his two aids, and his friend the publisher 
of the paper. He at last came to his 
early home, in America, and there died, 
leaving a record, short though it was, 
that most men might well envy. 

His work and the monuments of indus- 
try and ability which he has left behind 
him have peculiar interest to Americans; 
not simply because of his own connection 
with us by birth and early training, but 
because he never forgot his interest in 
his own country or his own countrymen. 
At a time when it was felt, by many 
of his colleagues in the profession and 
compatriots from the United States, that 
it was difficult to secure fair recogni- 
tion in England for good work done, or 
for the great inventions that were seek- 
ing continually to find introduction there, 
and when every one felt, visiting that 









country, that the feeling toward the 
American Cousin was not always kindly, 
and that the latter sometimes had reason 
to feel that he was not always, not often, 
in fact, given a generous reception, on 
that side the Atlantic, by those who 
should be his best and warmest friends, 
his brothers of the blood, Zerah Colburn 
told the writer that he intended that, 
in the columns of the new paper, especial 
care should be taken to give to America 
and to Americans ample spa'ce and fair 
hearing ; that the cousins from the West 
should have kindly welcome on all occa- 
sions, and a thoroughly honest and gen- 
erous treatment. National prejudice, 
mistaken patriotism, petty jealousy, 
should never shut out the brother-invent- 
or, the fellow-mechanic, the colleague 
in engineering of this side the Atlantic, 
from the English heart or British shops, 
so long as his journal should endure. 
And he well redeemed his promise ; and 
well have his heirs and assigns redeemed 
it. That attitude on his part preceded a 
very complete change in that of the Brit- 



ish press and the British people toward 
America and Americans,, and toward 
the work of the American engineer and 
mechanic. The devices of the " Yankee'* 
inventor are now nowhere more heartily 
and wholesomely received than by the 
better class of British technical journals. 
British practitioners have usually been 
fair and generous in their judgments of 
their cousins on this side the water. 

Colburn, as a matter of course, in or- 
ganizing and promoting a new scientific* 
periodical, found himself compelled to 
do a very large part of the work of writ- 
ing for the paper himself. But he se- 
cured, in this work, the aid and the= 
countenance of many of the best engineers, 
on both sides the ocean, and was espe- 
cially fortunate in obtaining the assist- 
ance of his old friend Alexander Holley, 
than whom no one could have wielded a, 
more facile and productive pen. The 
paper became promptly known in the 
United States as the friend of every 
American visiting London, and as the 
advocate of all worthy American enter- 



prises and inventions. Its circulation in 
the United States was promptly estab- 
lished, and it has never lost even its rate 
of gain in this constituency. But Col- 
burn never had the comfort of seeing 
ivhat a marvellous growth had come of 
the seed so hopefully, but desperately, 
planted by him. 

In the course of his work, he had paid 
much attention to the various depart- 
ments of steam-engineering, having been, 
ivith his friend Holley, especially inter- 
ested in railroads ; and this led him to 
the study of the subject of steam-boiler 
explosions, as one of peculiar importance 
and interest to the engineer as well as to 
the public. A suggestion made by Mr. 
Daniel Kinnear Clark, the now veteran 
engineer and author, led him to the de- 
yelopment of a theory of the method of 
explosion, in a certain class of cases, 
which has since been generally known 
as the Colburn Theory, or, more proper- 
ly, as the Theory of Clark and Colburn. 
It is this hypothesis which he sought to 
present clearly in the monograph on the 



8 



subject which is here printed and pub- 
lished. 

First published about I860, it remains 
the only special treatise on the Colburn 
and Clark Theory in the English lan- 
guage, and it has been thought by the 
publishers, and by many engineers as 
well, desirable that it should not be al- 
lowed to pass entirely out of print. This 
is the more advisable, that, in later years, 
new evidence has been obtained bearing 
upon that main argument, and, also, 
upon the thousand minor points which 
are grouped around it, in the study of the 
more general aspects of the phenomena 
of boiler decay and disruption. The 
writer, who happens to have paid some 
attention to the same subject, and to have 
collected considerable material into the 
form of a treatise of larger extent, recent- 
ly published, has been requested to edit 
this edition of tfyis little tract, for that 
most valuable series of monographs, the 
" Van Nostrand Science Series," and 
to add, in the form of footnotes, such 
references as may enable the reader who 



9 



may be sufficiently interested in the mat- 
ter to do so, to read evidence collected 
to date, in some detail. These references 
are mainly to the writer's larger work, 
"Manual of Steam-boilers; their 
Design, Construction, and Opera- 
tion," published in 1889 (last edition) 
by the Messrs. "Wiley, and sold by The 
Yan Nostrand Company. Where the 
reference is made to the "Manual" it 
is this treatise which is intended. 

Tor still other and detailed informa- 
tion, the reader may consult the little 
work of Mr. J. E. Eobinson, and the 
various fugitive essays to be found in peri- 
odicals, as referred to in the larger work 
to which reference is mainly had. The 
report on the work of Mr. Lawson, which 
is probably the first and only direct ex- 
perimental proof of the possibility of 
exploding a boiler by a process analogous 
to that which the far-seeing mind of Col- 
burn had indicated, will be found to 
be of extraordinary interest in this con- 
nection. The fulness with which origi- 
nal authorities have been cited in the 



10 



Manual makes it quite unnecessary to 
increase the bulk of this little tract by 
repeating them here. 

E. H. Thurstost. 

Director's Rooms, 
Sibley College, Cornell University, 
January 1, 1890. 



STEAM-BOILER EXPLOSIONS. 



A well-made steam-boiler cannot be 
burst or torn open except by a great force. 
The internal pressure required to rend 
open a cylindrical boiler may be approxi- 
mately calculated for any size of boiler and 
thickness of plates. With a boiler 3 ft. in 
diameter and 10 ft. long, the plates, iff 
in. thick and riyeted in the ordinary man- 
ner, oppose at least 65Jsq. in. of resisting 
section to any pressure tending to burst 
the boiler longitudinally open, or in the 
direction of its least resistance. A sec- 
tion of 65J sq. in. of iron, of average 
quality, would not yield under a tensile 
stress of much less than 1,462 tons (the 
resistance of the iron being taken as 
50,000 lbs. per sq. in.), and this amount 
of stress could not be exerted by the 
steam within a boiler of the assumed di- 
ll 



12 



mensions, except at a pressure of at least 
758 lbs. per sq. in. Such, a boiler, there- 
fore, if worked at a pressure of less than 
125 lbs. per. sq. in., would appear to be 
beyond all danger of explosion. 

This very large apparent margin of 
strength, has been taken by many as suffi- 
cient to justify the hypothesis of some vio- 
lent internal action, at the instant preced- 
ing the actual rupture of a steam-boiler; 
the rupture being regarded as the conse- 
quence of such, action, and not of a mere 
pressure; which., until the ruptured parts 
are in motion, can only act statically. 
In hypotheses of this kind, electrical ac- 
tion, the detonation of explosive gases 
assumed to be collected within the boiler, 
and the sudden production of steam from 
water thrown on hot plates, have been 
variously assigned as the causes of inter- 
nal concussion. Such hypotheses have 
derived a certain amount of probability 
from the fact that there are perhaps as 
frequent instances of the quiet rupture 
of steam-boilers as there are of their vio- 
lent explosion. A simple rupture, at- 






13 



tended only by the loss of the steam and 
water in the boiler, can of course occur 
only (under the ordinary working pres- 
sure) in consequence of the failure of a* 
particular plate or seam of rivets; either 
from original defects in the material, im- 
perfect construction, or from some injury 
which the boiler has sustained either at 
or before the moment of rupture. Such 
ruptures, being but rarely attended by 
any serious consequences, are seldom 
publicly reported. Their frequent occur- 
rence, however, might appear to exhaust 
the explanation by overpressure, so perse- 
veringly urged by Mr. Fairbairn and oth- 
ers in all instances of ;the violent explo- 
sion of steam-boilers. 

Without, however, at present consider- 
ing ourselves bound either to accept or to 
reject the explanation of steam-boiler ex- 
plosions by steadily accumulated pressure, 
we may consider the probability or other- 
wise of the various explanations which. 
assume the sudden production of great 
quantities of steam from water thrown 
upon red-hot plates; electrical action; the* 



14 



decomposition of steam and detonation 
of hydrogen in contact with air, etc. etc. 
Overheating. — Although it is possi- 
ble that boilers may be exploded, in con- 
sequence of the formation of a great 
quantity of steam from water thrown 
upon red-hot plates, * overheating cannot 
be assumed as being the general cause of 
explosions, which yery frequently occur 
where there is abundant evidence, both 
before and after the disaster, that no 
overheating has taken place. Explosions 
have happened in many cases when, but 
a moment before, the water-gauges indi- 
cated an ample supply of water; and in 
such cases, as well as in others, where 
there was positive evidence as to the 
amount of water in the boiler, the fur- 
nace-plates have been found in a per- 
fectly sound state, or at least without any 
appearance of having been burnt. Burnt 
iron can be recognized without difficulty, 
and the fact that the plates of an ex- 
ploded boiler show no signs of having 

* See Report of Committee of the Franklin Insti- 
tute ; Journal, 1836. Manual of Steam Boilers, p. 568. 



15 



been burnt may be taken generally as 
proof that they have never been over- 
heated after having been made up in 
the boiler of which they formed a part. 

Supposing, however, extensive and 
severe overheating to have taken place, 
and water to be suddenly thrown upon 
the heated plates, it is doubtful if the 
quantity of steam disengaged would be 
sufficient to increase greatly the pressure 
already within the boiler.* Whoever 
has observed a large mass of wrought 
iron, when plunged at a high heat into 
twice or three times its weight of cold 
water, must have remarked how small a 
quantity of steam was disengaged. There 
is reason to believe that just as much 
and no more steam would be- produced 
if the same weight of iron, heated to the 
same degree, were disposed in the form 
of a boiler, and the same quantity of cold 
water were suddenly thrown into it. If, 
however, the boiler already contained a 
considerable quantity of water, heated to 
from 212 deg. to 400 deg., the injection 

* Probably an error. See Manual, p. 567; § 277.— Ed. 



16 



of additional water, upon any overheated 
surface of the furnace might be followed, 
;as indeed, in such cases, it often is, by 
an explosion. The effects produced 
upon the sudden liberation of a great 
quantity of heat, stored up, under con- 
siderable pressure, in the water con- 
tained in a steam boiler, will be consid- 
ered in another part of the present paper. 
But there is, I think, sufficient reason to 
believe that an empty boiler, however 
much it may be overheated, may be filled, 
or partly filled, with water with no dan- 
ger whatever of explosion. Eed-hot 
boilers, I am told, have been occasion- 
ally filled in this way without any dis- 
turbance or consequences of any kind 
indicating a tendency to explosion. I 
have never tried such an experiment 
myself, nor can I, perhaps, furnish such 
authority as would, by itself, be sufficient 
to establish such a fact;* but a brief con- 

* A letter appeared in "The Engineer" of April 3d, 
.1857, signed " James Johnstone,' 1 and containing the 
following statement:— "In the course of my investi- 
gations I have obtained information that will be of use 
to your correspondent, 'J. H., jun.,' who, I perceive by 



17 



sideration of some of the phenomena of 
heat has convinced me that it is a fact. 
The actual quantity of heat which the 
thin metallic sides of a steam-boiler are 
capable of containing, is not sufficient to 
change a very large quantity of water 
into steam. According to the best au- 
thorities, the amount or total quantity 
of heat which would raise the tempera- 
ture of one hundredweight (112 lbs.) of 
iron, through one degree, would impart 
the same additional temperature to 12|- 
lbs. only of water. The quantity of heat 
which would raise the temperature of 
one hundredweight of copper through 
one degree would raise that of lOf lbs. 
only of water to the same extent. Thus, 

your last number, is about to fill a red-hot boiler with 
water by way of experiment. That has been done, and 
the result surprised the witnesses. The boiler was 25 
ft. long, 6 ft. diameter, and the safety-valve loaded to 
60 lbs. per sq. in. When empty and red-hot the feed was 
let on and the boiler filled up. No explosion occurred, but 
the sudden contraction of the overheated iron caused 
the water to pour out in streams at every seam and 
Fivet as far up as the fire-mark extended." In an edi- 
torial article which appeared in the " Scientific Ameri- 
can" some time in 1859, a similar experiment, attended 
by the same results, was also mentioned. 



18 



if we suppose a locomotive boiler to have 
500 lbs. of its copper plates heated to 
1,300 deg. (the melting point of copper 
being 2,160 deg.), this heat would be 
sufficient only to convert about 50 lbs. 
of water, already heated under the work- 
ing pressure to 350 deg., into steam; the 
water being thrown up, we may suppose, 
by violent ebullition, as when the com- 
munication between the boiler and the 
steam-cylinder of the engine is suddenly 
opened. The total heat of steam is a 
little more than 1,200 deg., although its 
sensible temperature, to which the cop- 
per plates would be cooled in evaporat- 
ing the water, is 414 deg. only at 275 
lbs. pressure, which pressure would cor- 
respond very nearly with the density of 50 
lbs. weight of steam when compressed into 
a steam-chamber of a capacity of 80 cu- 
bic feet, as in the larger class of locomo- 
tive boilers. And it must be under- 
stood that the whole quantity of dispos- 
able heat, as assumed above, must be 
appropriated by only 50 lbs. of water 
(assuming its temperature as 350 deg.), 



19 



in order [that it may be converted en- 
tirely into steam. If this quantity of 
heat be distributed throughout a greater 
quantity of water, less than 50 lbs. of 
steam will be produced, inasmuch as a 
portion of the heat which would be neces- 
sary to produce it will have been ab- 
sorbed in raising the temperature of the 
additional water, but without raising it 
into steam. It is plain enough that the 
quantity of heat which would be suffi- 
cient only to raise 50 lbs. of water into 
steam, would not suffice for converting 
any greater quantity of water, of the 
same temperature, into steam, and hence, 
with the quantities now assumed, 50 lbs. 
weight of steam could be produced only 
by the entire appropriation of the dis- 
posable heat, in the overheated plates, 
by 50 lbs. of water, and by the complete 
exclusion of this heat from any additional 
quantity of water admitted at the same 
time. If, therefore, the heat of 500 lbs. 
of copper plates at 1,300 deg. of tem- 
perature, were so far communicated to 
50 lbs. of water of 350 deg. as to raise it 



20 



into steam of 275 lbs. pressure and 
414 deg. temperature — the plates being 
cooled to the same temperature — the 
strain might, no doubt (added as it 
would be to the pressure of steam ex- 
isting in the boiler before the admis- 
sion of the water), burst it with all the 
violent effects of explosion. If, however, 
the situation of the overheated surfaces 
were such that a comparatively large quan- 
tity of cold water had to be admitted in 
order to cover a given area of hot metal, 
so that, by the time the 500 lbs. of cop- 
per were covered, 500 lbs. of cold water 
had been brought into contact with it, 
no steam could be formed, and the 
water would be raised by but about 100 
deg. of temperature. Any considerable 
quantity of water being present, its cir- 
culation would be so rapid that the heat 
applied to it at the bottom would be 
almost instantly communicated through- 
out its whole mass. This deduction from 
the accepted laws of heat is borne out, 
experimentally, in plunging any weight 
of highly-heated metal into an equal 



21 



weight of cold water* After the metal 
has been cooled to the temperature of 
the water, little or no evaporation of the 
latter will be found to have taken place. 
A pint claret-bottle, the glass of which 
is by no means strong, may, when filled 
with cold water, be safely held in the 
hand whilst a red-hot poker, as large 
as can enter the neck of the bottle, is 
plunged into the water. Not only will 
there be no explosion, but after the 
poker has been cooled to the temperature 
of the water, the latter, when shaken up, 
will have hardly more than a blood-heat, 
and none of the water will be evaporated. 
If the hot iron be kept from actual con- 
tact with the glass, this simple experi- 
ment may be repeated at pleasure without 
even cracking the bottle.* 

Much has been said of the spheroidal 
state of water when thrown upon heated 
plates. It would appear that, if ebulli- 
tion were delayed in such case until after 
a considerable quantity of water had been 
admitted, the heat of the plate would be 

* See Manual, p. 633, § 294; also § 279, as above. 



22 



so far absorbed in an equal or greater 
weight of water, that no explosion of the 
latter into steam could occur. This sug- 
gestion is given for what it is worth; but 
to my mind the spheroidal condition of 
water, under the circumstances men- 
tioned, has long been an argument 
against, rather than in favor of, the 
probability of explosion. * 

Superheated Steam. — When, how- 
ever, the plates of a steam-boiler are 
burnt, the steam which may be in con- 
tact with them becomes superheated.. 
Dr. Alban, in his work on the high- 
pressure engine, mentions that, in his 
practice, he often found tin-soldered 
joints in the steam-pipe melted by over- 
heated steam. Jacob Perkins heated 
steam, out of contact with water, to 
extraordinary temperatures, and it was 
his theory that, steam being similarly 
superheated when the water in a boiler 
is low, the subsequent agitation of the 
water, from any cause, instantly pro- 

* Manual, p. 582, § 282, for illustrations of violent ex- 
plosive action certainly due this cause. — Ed. 



23 



duces a large additional quantity of 
steam, and sufficient to cause explosion. 
In regard to the degree to which steam 
may be superheated, Mr. Longridge has. 
mentioned a case in his experience, a 
few years since, as Chief Inspector to 
the Manchester Boiler Association. In a 
boiler on which the steam-gauge marked 
a pressure of only 10 lbs. per square 
inch, the steam, held in contact with an 
overheated plate, became so highly super- 
heated as to completely char the wooden- 
lagging of the boiler, although the wood 
was entirely removed from any portion 
of the heating surfaces of the furnaces 
or flues. In a paper on the subject, 
read at the Institution of Civil Engineers 
in 1856, Perkins' theory of boiler explo- 
sions was reiterated at some length, and 
the writer (Mr. W. Kemble Hall) as- 
sumed that ordinary steam, superheated 
to say 435 deg., would instantly convert 
water, thrown among it, into steam of a 
pressure of 360 lbs. per square inch. 
The fact was overlooked, no doubt, that 
75 cubic ft. of steam, at a pressure of 



24 



140 lbs. per square inch, weigh but 26 
lbs., and that the specific heat of steam, 
at ordinary temperatures, is less than 
one-third that of water. Thus all the heat 
contained in 26 lbs. of steam, in a loco- 
motive boiler, supposing the steam super- 
heated even to 350 deg. above the tem- 
perature due to its pressure, could not 
generate much more than 3 lbs. of addi- 
tional steam, which weight of steam, in 
the boiler in question, would not raise 
the pressure, at 140 lbs., to more than 
160 lbs. to the square inch. Without 
pretending to any exactness in these 
figures, it is apparent upon a little con- 
sideration that the conversion of water 
into steam, by being thrown up in a 
divided state, into highly superheated 
steam, can hardly ever be 'sufficient of 
itself to account for any boiler explosion.* 
Dr. Alban has stated that in some of his 
experiments with a steam-generator, he 

* In the Repertory of Patent Inventions, Supple 
ment, January, 1832, page 424, Mr. Thomas Earle gave 
the results of a calculation similar to the above, and 
tending to disprove Perkins' theory, at that time being 
urged. 



25 



stopped the injection of water and kept 
the enclosed steam in contact with a 
metallic surface at a temperature of 800 
deg., and yet no symptoms of an explo- 
sion appeared when the water was re- 
introduced. He adds that a long-con- 
tinued injection was necessary before 
enough pressure could be obtained to 
set the engine at work again. 

It is, nevertheless, a favorite opinion 
with many engineers that the presence 
of highly superheated steam within a 
boiler is sufficient to account for the 
most violent explosion. As compared 
with other current explanations of 
boiler explosions, it is perhaps no dis- 
advantage to the explanation by super- 
heated steam that it is incapable of 
proof. Although any one may blow up 
a boiler, no one has been able to prove, 
either by experiment or by calcula- 
tion, that superheated steam, decom- 
posed steam, or even electricity, could 
produce such a result. If, on the other 
hand, we proceed to investigate the prop- 
erties of steam, under various conditions^ 



26 



"with such aids as science has placed at 
our disposal, we may satisfy ourselves 
"that the explanations in question are er- 
roneous ; and it is quite capable of proof 
by experiment that they are so. It is 
evident enough that no heat can be 
generated within the steam- or water- 
chamoer of a boiler. All the heat which 
may exist there must have been com- 
municated from an external source — that 
is to say, from the fuel burning in the 
furnace. Heat acts by its quantity, 
just the same as ponderable matter ; 
and, so far as its effects are concerned, 
heat is as measurable as a solid body. 
If we cannot conceive the material exist- 
ence of heat, we may observe, by the 
simplest experiment — that of plunging a 
hot poker into a pail of water — that a 
given weight of metal, heated to a given 
incandescence, will always impart a 
definite, and the same elevation of tem- 
perature to a given weight of the cooling 
•or absorbing medium. The quantity of 
heat which will raise a pound of water 
through 1 deg. of temperature is as 



i 



27 



definite and invariable as the quantity of 
water which will fill a given space, or as 
the weight, at any height of the barome- 
ter, of the air we breathe. 

ISTo one, perhaps, would deny these 
well-known truths in the abstract, and I 
must plead, as my excuse for repeating" 
them, the general oversight of such facts 
in the explanation of boiler explosions 
by superheated steam. Although the 
sum of the sensible and latent heat of 
ordinary steam is not constant at all 
pressures, it is nearly so. Practically,, 
steam not superheated cannot lose any 
part of its heat without being more or 
less condensed. In other words, it can- 
not make an additional quantity of 
steam; since, to do so, it would requiro 
to possess the power of producing and 
communicating an amount of heat which, 
it did not previously contain. Steam 
may be led from one vessel and made to 
boil water in another, but this is only a 
transference of steam, as all the steam 
formed in the second vessel will disap- 
pear from the first, and as much more 



28 



besides as was required to raise the water 
in the second to the boiling point. With 
ordinary steam, the injection of any 
quantity of water, cooler than itself, 
timong it, is attended with a partial con- 
densation of the steam, and the eleva- 
tion of the temperature of the water, but 
never by the production of additional 
steam. The quantity of heat which will 
raise 1 lb. of water through 1 deg. being 
termed an "unit of heat," about 1,150 
units will be required to convert 1 lb, 
of water, at 60 deg., into steam. But if 
the heat for conversion come from super- 
heated steam (and it must be super- 
heated, in order to generate additional 
steam, since it can part with none of its 
ordinary or normal heat without more or 
less conpensation), we then find that, 
owing to the difference between the 
specific heat of steam and that of water, 
.a pound of the former must be super- 
heated by nearly 3,500 deg., in order to 
impart 1,150 units of heat to a pound of 
the latter ; at the same time maintain- 
ing its own existence as steam. Consid- 



29 



ering that an ordinary locomotive boiler 
seldom contains 25 lbs. of steam, disen- 
gaged from the water, and that even 
1,000 deg. of superheating in addition 
to from 300 deg. to 350 deg., the ordi- 
nary temperature of the steam, would be 
excessive, the explanation by super- 
heated steam appears sufficiently incom- 
plete to warrant its rejection. 

The foregoing reasoning upon the pro- 
duction of steam from water thrown 
upon red-hot plates was first suggested 
to me by Mr. D. K. Clark ; although 
I understand Mr. Clark to hold the 
opinion that the steam thus produced 
cannot be sufficient to account for boiler 
explosions. Under certain circumstan- 
ces, I believe a boiler may be violently 
exploded by the steam thus formed, and 
I think the explanation by overheating 
possesses considerable probability, al- 
though it cannot, of course, be adopted in 
those frequent cases where there is proof 
that no overheating has taken place.* 

* Manual, p. 559, §§ 275-276 ; in which are described 
the corroboratory experimental work of Lawson. — Ed. 



30 



Electricity.— The well-known fact that 
steam sometimes exhibits electrical prop- 
erties on being discharged into the air, 
no doubt suggested the electrical hy- 
pothesis of boiler explosions. Those, 
however, who have adopted this hy- 
pothesis are unable to furnish any evi- 
dence of the existence of free electricity 
within a steam-boiler. All our knowl- 
edge of electricity goes to show that 
even if it were developed by ebullition, 
or in steam when confined under pres- 
sure, it could not collect within a metallic 
vessel, which, like a boiler, is in perfect 
electrical communication with the earth. 
The electrical phenomena sometimes ob- 
served when steam is being discharged 
into the air are believed to be caused 
partly by the friction of the escaping 
steam upon the inner surfaces of the dis- 
charging channel ; whilst it is possible 
that electricity is also liberated in the 
condensation of steam in the open air. 

Professor Earaday has examined with 
great care the action of Armstrong's 



31 



hydro-electric engine,* in which steam, 
generated from distilled water in a boiler 
insulated upon glass supports, produces 
electricity on being discharged through 
a peculiar apparatus into the air. The 
steam is led by a pipe from the boiler, 
and through three or more small pas- 
sages surrounded with a cooling appa- 
ratus, by which the steam is partially 
condensed into drops of water. In this 
state it enters, by tortuous passages, a 
series of discharging nozzles, each of 
which has an internal bushing or lining 
of box-wood. On the final discharge of 
the steam from these nozzles into the air, 
electricity is disengaged, and is collected 
by suitable metallic points connected 
with an ordinary conductor. Although 
powerful discharges can be thus ob- 
tained, there is no evidence whatever of 
the presence of electricity within the 
boiler. Indeed it is only by certain 

* The hydro-electric engine in the "Conservatoire des 
Arts et Metiers," at Paris, is the only one of the kind 
that I have seen, and I have taken the results of Pro- 
fessor Faraday's examination of the machine from 
Gavarret's "Traite d'Electricite," Paris, 1857.— Z. C. 



33 



yery peculiar arrangements that electric- 
ity is obtained at all. Professor Faraday 
found that if, instead of distilled water, 
ordinary spring water, containing the 
usual proportion of atmospheric air, was 
employed ; or, if any saline, acid, or 
alkaline substance capable of acting as a 
conductor, was dissolved in the water in 
the boiler, there was no electricity to be 
had. Nor did the conductor become 
charged unless the process of partial con- 
densation was maintained in the " re- 
frigerating box ;" and, what was more 
singular, nothing but lox-wood nozzles 
appeared to have the power of finally ex- 
citing the electrical action at the instant 
of discharge. 

The results of Professor Faraday's re- 
searches, as to the mode in which elec- 
tricity was produced in the experiments 
which he made with Armstrong's ma- 
chine, comprise the following facts: — 

1. The production of electricity is not 
due to any change in the state of tha 
liquid contained in the boiler. 

2. A current of dry steam produces no 



33 



development of electricity. The pro- 
duction of electricity is due to the fric- 
tion in the box-wood nozzle of the drops 
of water, formed by the partial conden- 
sation of the steam in the refrigerating 
box. 

3. Increasing the pressure of the steam 
increased the development of electricity 
by increasing the friction of the issuing 
jets of steam and water. 

4. The same results were obtained from 
compressed air, discharged through the 
box-wood nozzles, as from steam dis- 
charged under the same circumstances. 
When the air was perfectly dry there was 
no development of electricity; when the 
air was humid, and contained besides a 
very little pulverulent matter, the fric- 
tion of discharge produced electricity in 
the same manner as when steam was em- 
ployed in the experiments. 

It will be borne in mind that with all. 
the special and peculiar conditions requi- 
site for the production of electricity by 
this apparatus, the boiler must be per- 
fectly insulated on glass supports. And 



34 



although Mr. Armstrong probably con- 
structed his machine under the impres- 
sion that the generation of steam was 
essential to the results sought to be 
obtained, Professor Faraday found that 
the same results were disclosed when 
atmospheric air, condensed to the same 
pressure as the steam, was employed in 
its stead. 

It has been ingeniously argued that 
steam-boilers may become insulated by an 
internal coating of boiler-scale. It would 
be necessary, however, that this scale 
should completely cover every part of the 
internal surfaces of the boiler, and even 
those of the steam-pipe, stopcock, etc. 
A single crack in any part of this com- 
plete dielectric lining would liberate any 
electricity which might be contained in 
the steam. Whilst there is no proba- 
bility that any steam-boiler was ever so 
completely lined with scale, there is 
another fact which appears to dispose 
of the electrical explanation, even if per- 
fect insulation existed. This fact is, 
that water may be boiled in a perfect 



35 



Leyden arrangement with no develop- 
ment of electricity. 

Without pursuing the electrical hy- 
pothesis any further, we may observe 
that no one has yet offered to explain 
how electricity, even if it existed in high 
tension, would explode a steam-boiler. 
And, if it exist at all in steam-boilers, 
why does it not exist in all boilers ? And 
if in all, why does it not manifest its 
presence in other ways than in explo- 
sions? If electricity act at all it must be 
by quantity, and if the quantity devel- 
oped be sometimes sufficient to burst 
boilers, we have a right to look for visi- 
ble, although milder, phenomena when 
the quantity is insufficient. Yet no phe- 
nomena of the kind, sufficient to excite 
alarm, or even to attract attention, are 
observed. The fact is, no one has elabo- 
rated the electrical hypothesis into any- 
thing like a theory of boiler explosions. 
The presence of electricity has been sug- 
gested, and among those who prefer mys- 
tery, or, at least, very obscure explana- 
tions, to circumstantial investigation^ 



36 



some have referred boiler explosions to 
electricity. 

Decomposed Steam. — The unsatisfac- 
tory results generally obtained by those 
who have sought to decompose water 
by heat, on a large scale, with the view 
of applying its elementary gases sepa- 
rately, does not appear to have prevented 
the occasional adoption of the hypothesis 
that, in certain cases, all the steam con- 
tained within a boilar is decomposed, 
and its hydrogen (by some means not 
easily explained) exploded with great 
violence. That steam, passed over pure 
metallic iron heated to redness, is de- 
composed is perfectly true, although the 
iron must retain all the oxygen separated 
in the operation. With oxidized iron, 
however, the process of decomposition 
cannot be continued. This is, I believe, 
a chemical fact of which there can be no 
dispute. To decompose 1 lb. of water 
(or steam, which is chemically the same 
substance), 14.2 oz. of oxygen must be 
fixed by the iron, and only 1.8 oz. of 
hydrogen 7 will be set free. This large 






37 



proportion of oxygen, absorbed by only a 
few square feet of overheated surfaces, 
would soon form an oxide of iron of 
sufficient thickness to arrest all further 
decomposition, and all the hydrogen up 
to that time disengaged would not 
amount, perhaps, to 1 lb. in weight. 
By itself, or mixed with steam, hydrogen 
cannot be exploded, nor even ignited. 
It will extinguish flame as effectually as 
would water. 

Upon this subject, I may refer to a 
report made by Professor Faraday in 
May, 1859, to the Board of Trade, upon 
the liability to accident consequent upon 
the introduction of an apparatus for 
superheating steam on board the Wool- 
wich steamboats. In this apparatus the 
steam was carried, in iron pipes, imme- 
diately through the furnace and in con- 
tact with the incandescent fuel. Pro- 
fessor Faraday, after having examined 
the apparatus at work, says : — 

"I am of opinion that all is safe, i.e., 
that as respects the decomposition of the 
steam by the heated iron of the tube, and 



the separation of hydrogen, no new danger 
is incurred. Under extreme circum- 
stances the hydrogen which could be 
evolved would be very small in quantity 
— would not exert greater expansive force 
than the steam — would not with steam 
form an explosive mixture — would not be 
able to burn with explosion, and proba- 
bly not at all if it, with the steam, escaped 
through an aperture into the air, or even 
into the fire-place. 

e( Supposing the tubes were frequently 
heated over-much, a slow oxidation of 
the iron might continue to go on within; 
this would be accompanied by a more 
rapid oxidation of the exterior iron sur- 
face, and the two causes would combine 
to the gradual injury of the tube. But 
that would be an effect coming under the 
cognizance of the engineer, and would 
require repair in the ordinary way. I do 
not consider even this action likely to 
occur in any serious degree. I examined 
a tube which had been used many months 
'which did not show the effect; and no 



39 



harm or danger to the public could hap- 
pen from such a cause. " 

Professor Taylor, of Guy's Hospital, 
reported in part, as follows, upon the 
same apparatus: — 

"It is true that steam passed oyer 
pure metallic iron heated to redness 
(1,000 deg.), is so decomposed that the 
oxygen is fixed by the iron while hydro- 
gen gas is liberated. This chemical ac- 
tion, however, is of a very limited kind. 
The surface of the iron is rapidly covered 
with a fixed and impermeable layer of 
the magnetic oxide of iron, and thence- 
forth the chemical action is completely 
arrested. If the interior of an iron pipe 
has been already oxidized, by passing 
through it, while in a heated state, a cur- 
rent of air, there will be no decomposi- 
tion of steam during its passage through 
it. If the interior of an iron pipe were 
not thus previously oxidized, it would 
speedily become so by the oxygen derived 
from the air, which is always mixed with 
steam. Hence, chemically speaking, un- 
der no circumstances, in my opinion, 



40 



would any danger attend the process of 
superheating steam, as it is conducted 
under this patent. 

" It is proper also to state,." that hydro- 
gen is not explosive, but simply combus- 
tible, and assuming that it was liberated 
as a result of the decomposition of super- 
heated steam, its property of combusti- 
bility would not be manifested in the 
midst of the enormous quantity of aque- 
ous vapor liberated with it and condensed 
around it. There could be no explosion, 
inasmuch as hydrogen, unless previously 
mixed with oxygen, does, not explode; 
and oxygen is not liberated; but actually 
fixed by the iron in this process. It is a 
demonstrable fact that the vapor and gas 
evolved under the form of superheated 
steam, tend to extinguish flame and 
to prevent combustion from any other 
cause." 

Professor Brande, in a report made by 
him to the patentees of the same appara- 
tus, observes: — 

" In reference to the question which 
you have submitted tome, respecting the 






41 



possible or probable evolution of hydrogen 
gas and consequent risk of explosion in 
the processes and by means of the appara- 
tus which you employ for the production 
of superheated steam, I am of opinion 
that there can be no danger from such 
effect ; that the temperature to which the 
iron pipes connected with your boiler are 
raised, and the extent of the iron surface 
oyer which the steam passes, are insuffi- 
cient for its decomposition ; and that if 
the temperature of the pipes were eyen 
raised considerably beyond that which 
you employ, or would be able to attain, 
n superficial layer of oxide of iron would 
line the interior of the heated pipes, and 
so prevent any continuous decomposition 
of water. Effectually to decompose steam, 
by passing it over iron, it is necessary 
that a very extended surface of the metal 
(as in the form of thin plates or iron 
turnings) should be used, and that the 
temperature should be continuously main- 
tained at a bright red heat, namely at a 
temperature considerably above 1,000 deg. 
of Fahrenheit. 



42 



« I have read Dr. Taylor's report, and 
entirely agree with the inferences he has 
drawn as to the absence of danger from 
the evolution of hydrogen gas in practi- 
cally carrying out your process for the pro- 
duction and application of superheated 
steam." 

The practical conclusions upon this sub- 
ject are the following: — 1. Decomposition 
cannot possibly occur, to any considerable 
extent, under any circumstances arising in 
the working of ordinary steam-boilers; 2 y 
If it did occur, the hydrogen thus liber- 
ated would have no access to oxygen, 
without which it could neither inflame 
nor explode ; 3, Even if oxygen were 
present, the presence of steam would pre- 
vent ignition ; and, 4, If oxygen were 
present, and no steam existed in the 
boiler, the hydrogen would only inflame 
and burn silently as fast as it was pro- 
duced, the heat for ignition being sup- 
posed to come from a red-hot plate. 
Under these accumulated impossibilities 
of violent explosive action, the explana- 
tion of boiler explosions by thedecompo- 



43 



sition of steam is without any support 
whatever. 

Overpressure. — Any pressure, whether 
gradually or momentarily generated in 
a boiler, is an overpressure when it ex- 
ceeds the safe working pressure ; and, 
strictly speaking, there must always be 
overpressure whenever a boiler is burst. 
When, however, an explosion i s said to 
have occurred by overpressure, it is com- 
monly understood that the pressure has 
heen allowed to increase gradually up to 
the limit of the strength of the boiler, 
and if this has been calculated to corre- 
spond to a pressure of 700 lbs., for in- 
stance per square inch, the actual pressure 
at the moment of explosion is accordingly 
assumed at that moment. Boilers may, 
perhaps, be generally capable of with- 
standing nearly their full calculated 
bursting pressures ; indeed, comparative- 
ly few boilers do fail in any way, for after 
all, the number of explosions — numerous 
as they are — bears but a very small pro- 
portion to the actual number of boilers 
in use. But for the purposes of investi- 



u 



gation, there are abundant instances of 
the quiet rupture of steam-boilers under 
ordinary working pressures, so that even 
a violent explosion does not absolutely 
prove that the pressure under which it oc- 
curred was anything like the calculated 
bursting pressure of the boiler. If the 
bursting pressure be 758 lbs. per square 
inch it might not be difficult to raise the 
steam to that point and burst the boiler. 
Yet it is very improbable that anything 
like a pressure of 758 lbs. per square inch 
ever accumulates in a boiler intended to 
work at 100 lbs. or 125 lbs. We will 
suppose a locomotive boiler with 75 cu- 
bic ft. of water-room containing 4,650 lbs. 
of water, and 75 cubic ft. of steam-room 
containing 23 lbs. in weight of steam at 
a pressure of 120 lbs. per square inch. 
To increase the pressure even to 285 lbs. 
per square inch, 25 1 lbs. additional weight 
of steam would have to be compressed into 
the steam-chamber, and the remaining 
4,624^- lbs. of water would have to be 
raised to 350 deg., the temperature of 
steam of 120 lbs. to 417-J- deg., the tern- 



45 



perature of steam of 285 lbs. pressure. 
The 25f lbs. of additional steam, formed 
from water of an average temperature of 
380 deg., would have absorbed about 
21,000 units of heat, whilst the elevation 
of the temperature of 4,624 lbs. of water, 
by 67^- deg., would require 312,120 units 
of heat. The whole heat thus expended 
w^ould equal that necessary for the evap- 
oration of about 285 lbs. of water under 
a moderate pressure, and this heat would 
require the combustion of at least 32 lbs. 
of good coke. Although the steam-gauge 
of a locomotive will often rise 7 lbs. 
or 8 lbs. a minute in standing, and 10 
lbs. or even 15 lbs. when a strong blast 
is turned up the chimney when running 
with a light load, the steam could not 
probably rise from 120 lbs. to 285 lbs. in 
much less than twenty minutes under 
any circumstances likely to occur in prac- 
tice. Mr. Eairbairn has calculated that 
with a certain locomotive boiler on which 
he experimented, 43 minutes would be 
required to raise the pressure from that 
of the atmosphere to 240 lbs. With the 



46 



same boiler under the same circum- 
stances as in the first experiment, 28 
minutes would be required to raise the 
pressure from 60 lbs. to 300 lbs. per 
square inch. The rapidity with which 
the steam-pressure would rise would al- 
together depend upon the relative extent 
and temperature of the heating surface 
to the quantity of water in contact with 
it. Mr. Martin Benson, who has had 
much experience in the working of the 
steam fire-engines employed at Cincin- 
nati, United States, informs me that, 
with the fires carefully laid with light 
combustible materials, steam has been 
raised in the boilers of these engines in 
4 min. 38 sec, from cold water to a 
pressure of 65 lbs. per sq. in. In 2 min. 
the pressure has been raised from 10 lbs. 
to 90 lbs. per sq. in. In these boilers, 
however, the tubes are first heated, and 
small quantities of water are afterwards 
injected into them, the whole quantity 
of water at any time in the boiler rarely 
exceeding one cubic foot.* 

* Manual, p. 589, §283; exhibiting the fact of such. 



47 



The simple increase of pressure in a 
boiler, either when at work or when 
standing, must undoubtedly be compara- 
tively gradual — a matter of some min- 
utes, at least. "Whatever might cause the 
steam-gauge to mount, suddenly, from 100 
lbs. to the limit to which it is marked, it is 
very certain that the necessarily gradual 
increase of the heat of the water within 
the boiler could not produce such a re- 
sult. Yet those who have given any at- 
tention to the subject of boiler-explosions, 
are aware that they frequently occur 
when, without any overheating of the 
plates, the pressure stood, but a moment 
before, at the ordinary working point. In 
the case of the locomotive boiler which ex- 
ploded in the summer of 1858, at Messrs. 
Sharp, Stewart & Co/s, at Manchester, 
the pressure, as observed upon two spring 
balances and a pressure-gauge, stood at 
117 lbs. to 118 lbs., a minute before the 
explosion, both valves blowing off freely at 
the time. The part of the boiler which 

explosions occurring, and presenting the computations- 
—Ed. 



48 



exploded was the ring of plates next the 
smoke-box, out of the influence of any 
part of the fire. The fact, therefore, of 
the violent explosion of a strongly made 
boiler at 117 lbs., is a proof that it is 
not necessary to assume and to account 
for the existence of any pressure about 
that point. On the 5th of May, 1851, a 
locomotive engine, only just finished, 
burst its boiler in the workshop of Messrs. 
Rogers, Ketehum & Grosyenor, at Pater- 
son, New Jersey, United States. I was 
upon the spot but a few moments after- 
wards, and found the effects of the ex- 
plosion to be of the most frightful char- 
acter : a considerable portion of the three- 
story workshop being blown down, whilst 
four men were instantly killed, and a 
number of others were injured, one of 
whom died soon afterwards. Several of 
the men, who, although immediately 
about the engine at the time, escaped 
unhurt, unanimously declared that the 
safety-valves were blowing off before the 
explosion, and that the two spring bal- 
ances indicated, but a moment before 



49 



the crash, a pressure of but 110 lbs. per 
sq. in. On the 12th of February, 1856, 
the locomotive Wauregan exploded, after 
standing for upwards of two hours in 
the engine-house of the Hartford, Provi- 
dence, and Fishkill Eailroad, at Provi- 
dence, United States. Only sufficient 
steam had been maintained in the boiler 
to enable the engine to be run out of the 
house; but at the time of the explosion 
the engine had not been started, the en- 
gine-man, who was killed, being upon 
the floor, at the side of the engine, at 
the time. The boiler gave out in the 
ring of plates next behind the smoke- 
box.* Destructive explosions often oc- 
cur at pressures of 10 lbs. to 12 lbs. per 
sq. in. in low-pressure boilers ; and it is 
on many accounts improbable that any- 
thing like the calculated bursting pres- 
sures of boilers is ever reached, even 
where the most frightful explosions have 
occurred. Not only would the accumu- 
lation of steam of the calculated bursting 
pressure require considerable time, but 

* Manual, § 281, p. 581, for account of this case.— Ed. 



50 



the gauge, if there were one, would soon 
be fixed at the limit of its motion, and 
the safety-valves, if they were not wedged 
down, would blow off with unusual vio- 
lence. In the case of locomotive en- 
gines, which have no self-acting govern- 
ors, any considerable increase of pres- 
sure would, if the engine were under 
way, quicken its speed, and cause the 
driving-wheels to slip upon the rails to 
such an extent as to arrest the attention 
of the engine-man. The fact that he 
would have to nearly close the regulator, 
and keep it nearly closed, whilst drawing 
a load with which it was at other times 
necessary to run with the regulator wide 
open, would be a significant indication 
of the state of things in the boiler. 

If boilers burst only from overpres- 
sure, they would, of course, give out 
first — as, indeed, they always must — in 
the weakest part ; say, along a seam of 
rivets, which is but about one half as strong 
as the solid plate. But, after one seam 
had opened, the relief of pressure would 
be so instantaneous that, without subse- 



51 



quent percussive action, the rupture could 
hardly extend itself through solid plates 
of nearly twice, or even, perhaps, ten 
times the strength of the part which first 
gave way. The general strength of the 
solid plates of a boiler should be, and 
probably is, from ten to twenty times 
greater than that of any part so weak as 
to rupture, as is often the case, under 
the ordinary working pressure. Mr. 
Whitworth has made an experiment upon 
one of his new cannon, made of homo- 
geneous iron, which shows how a great 
pressure may relieve itself by a very 
small opening. After loading one of his 
3-pounders, he plugged the muzzle so as 
to render it impossible for the gun to 
discharge itself in the ordinary manner. 
On firing the charge the piece did not 
burst, but all the gases escaped through 
the e f touch-hole." This severe test was 
repeated several times. In the case of 
excessive pressure, there would be many 
circumstances to attract the attention of 
the attendants, whereas explosions more 



52 



commonly occur with little or no warn* 
ing whatever. 

This line of argument tends, undoubt- 
edly, to assimilate the conditions of vio- 
lent explosion to those of quiet rupture; 
and although like causes should produce 
like effects, it may perhaps be shown 
that, so far as pressure alone is con- 
cerned, either explosion or simple rup- 
ture may occur indifferently at one and 
the same actual pressure, existing up to 
the moment of failure. Instead, there- 
fore, of calculating the strength of a 
boiler from its diameter and the thick- 
ness of the plates, and then assuming 
that it can only burst at a corresponding 
pressure, I shall adopt the fact of quiet 
or simple ruptures as proving (what 
might, indeed, be taken for granted) 
that boilers are not always as strong as 
they are calculated to be; and I shall 
then endeavor to show how violent ex- 
plosion may result in one case from a 
pressure which only causes quiet rupture 
in another. 

Strength, of Heated Iron. — Overheat- 



53 



ing, which has been considered with ref- 
erence only to the generation of steam 
from water suddenly thrown on heated 
plates, and with reference to the decom- 
position of steam, may materially reduce 
the strength of boiler-plates. Up to 
temperatures of 400 deg. and 550 deg. 
boiler-plates have not been found to be 
weakened ; indeed, the experiments of 
the Committee of the Franklin Institute 
indicated a gradual gain of strength, 
with increasing temperatures, up to a 
certain point, and that the strength at 
550 deg. was equal to that at 55 deg. 
Mr. Fairbairn finds the strength dimin- 
ished one-fourth at a red heat ; and it is 
not difficult to understand that, at a very 
high heat, no reliance whatever could be 
placed upon iron or copper when sub- 
jected to strain.* The furnace-flues of 
Cornish boilers, and the crown-plates of 
locomotive boilers, frequently alter their 
shape when overheated, and are often 
continued in regular work, until from 

* Manual, p. 5G8 ; § 278, and for detailed account of 
loss of strength by heat, especially, p. 83, § 37. — Ed. 



54 



some cause — another burning, perhaps— 
they give out entirely. Although an. ex- 
amination of the furnace-plates, recov- 
ered from an explosion, often shows that 
they have never been subjected to an in- 
jurious temperature, overheating must 
be taken as one among the various causes 
which may operate to weaken a steam- 
boiler. 

Tests by Pressure. — Again, as it is 
considered injurious to a boiler to prove 
its strength, before it is put under 
steam, by a great hydrostatic pressure, 
we have no better means of ascertaining 
its actual strength than by inferring the 
bursting pressure from its dimensions, 
and from the thickness and general 
quality of the plates. Indeed, the actual 
strength of a boiler can be ascertained 
only by a process which involves its de- 
struction. In other words, pressure of 
some kind must be accumulated within 
it until it bursts, in order to know what 
amount of pressure will suffice to burst 
it. A new locomotive boiler, of peculiar 
construction, which exploded in Octo- 



55 



ber, 1856, at Messrs. Bolckow & Vaugh- 
an's ironworks, at Middlesborough-on- 
Tees, was believed to have been injured 
in a previous test, by steam-pressure of 
130 lbs. per sq. in.* Dr. Joule, of Man- 
chester, has lately called attention to the 
liability to injury to which boilers are 
exposed under tests by steam or hydro- 
static pressure. He proposes a test em- 
ployed by himself with entire success for 
the last two years. He fills the boiler 
entirely full of water, and then makes a 
brisk fire upon the grate. When the 
water has been warmed to from 70 deg. 
to 90 deg., the safety-valve is loaded to 
the pressure up to which the boiler is to 
be tested. The rise of pressure is then 
carefully observed by a steam-pressure 
gauge; and if the progress of the pointer 
be constant and uniform, without stop- 
page or retardation, uip to the testing 
pressure, it is inferred that the boiler 
has withstood it without strain or incipi- 
ent rupture. In this mode of testing, 

* See Manual, p. 601, § 287, for illustration in case of 
the ' ' Westfield . ' '—Ed. 



56 



the expansion of the water, by heat, is so 
rapid, that Dr. Joule has found the 
pressure to rise from zero to 62 lbs. per 
sq. in. in fire minutes. But this mode 
of testing the strength of a boiler can- 
not, any more than any other mode, 
show the strength beyond the testing 
pressure; it cannot show the actual 
strength or bursting pressure of the 
boiler except that be destroyed in the 
test. And although the quality of the 
materials and workmanship in steam- 
boilers may vary generally within nar- 
row limits only, not only different boil- 
ers, but different parts also of the same 
boiler, are of very unequal strength. 
The weakest part of the weakest boiler 
may be almost immeasurably weaker 
than the strongest part of the strongest 
boiler. The material of which boilers 
are made varies greatly in strength. In 
Messrs. E. Napier & Sons' recent experi- 
ments (conducted by Mr. David Kir- 
kaldy) upon the strength of iron and 
steel, one sample of Parnley plate iron 
bore a strain of 62,544 lbs. per sq. in., 



57 



whilst another sample of iron from the 
same makers broke under a strain of 
40,541 lbs. per sq. in. Glasgow ship- 
plates bore, in one case, 53,370 lbs. per 
sq. in. and in another only 32,440 lbs. 
Even Lowmoor iron varied in strength 
between the limits of 47,426 lbs. and 
57,881 lbs. per sq. in. However the 
strength of iron may be averaged for the 
general purposes of the engineer, we are 
never justified in assuming an average 
or standard strength for the particular 
parts of a steam-boiler which, in the case 
of explosion, were the first to give out. 
The fact of explosion is in itself prima 
facie evidence that these parts were not 
of average strength, and affords good 
ground for the presumption that they 
were of only the minimum strength; 
and the minimum strength of iron is 
not known, for however weak a given 
specimen might be, another one, much 
weaker, might doubtless be found. 
Comparatively, few experiments have 
ever been made upon the strength of 
plates, and the averages given by Mr, 



58 



Fan-bairn and others have been taken 
from comparatively few trials. Messrs. 
Napier's experiments were considered 
very comprehensive; yet they included 
only 150 specimens of iron plates, with 
which number the range of strength was 
from 32,450 lbs. to 62,544 lbs. per square 
inch. Mr. Fairbairn found the strength 
of a broken plate, taken from the boiler 
which exploded at Messrs. Sharp, Stewart 
& Oo/s, to be only 4.66 tons per square 
inch, or but one-fifth of the proper aver- 
age. It is presumable, perhaps, that the 
strength of plate iron varies within as 
wide limits as that of cast iron, from 
which plate iron is made, and upon the 
quality of which its own must also de- 
pend. The Government cast-iron experi- 
ments concluded last summer, at Wool- 
wich, comprised 850 specimens, ranging 
in strength from 9,417 lbs. to 34,279 lbs. 
per square inch, the average strength of 
all the specimens being 23,257 lbs. It 
must be remembered, however, that the 
sample which bore only 9,417 lbs. per 
square inch cannot be taken as the weak- 



59< 



est which would occur in practice, inas* 
much as it was not selected at random 
from iron in the market, but was one of 
several samples which had been con- 
tributed by a long-established firm, with 
the expectation, no doubt, of obtaining 
the preference of the authorities. If the 
poorest iron were purposely sought for, 
as it should be, in order to estimate the 
chances of failure, cast iron could, no 
doubt, be found which would not bear a 
strain of 3, 000 lbs. per square inch; whilst, 
on the other hand, there are authenti- 
cated instances of tests in which cast iron 
did not yield until the strain had reached 
45,000 lbs. per square inch. 

Apart, also, from the quality of the 
iron, its thickness varies greatly in the 
practice of various makers. In the 
United States, for example, the plates 
in the waist of a locomotive boiler, 48 in. 
in diameter, and intended to carry steam 
of 120 lbs. per square inch (sometimes 
increased to 160 lbs. or more), are |- in. 
only, although ^ in. plates are occasion- 
ally used. In England, the thickness of 



60 



plates for such a boiler is from f in. to 
^ in. ; T \ in. being a common thickness. 
In France a 48-in. locomotive boiler, the 
pressure within which rarely exceeds 120 
lbs., is generally 15 millimetres, or ^ in. 
thick. The strongest form of a boiler is 
a, homogeneous metal tube, drawn solid, 
and of from say 1|- in. to 2 in. diameter. 
Its bursting pressure is seldom less than 
7,000 lbs. per square inch; in some cases, 
as much as 15,000 lbs. 

In working iron into steam-boilers, it 
is commonly supposed that the loss of 
strength in punching is proportional 
only to the width punched out. If, in a 
row of rivet holes, in the edge of a plate 
24 in. wide, there are 13 holes of f in. 
diameter, the length of iron removed in 
the line of strain is 13 X f = 9f sq. in., 
or but about two-fifths of the whole 
width of the plate. Mr. Fairbairn has 
found, however, that the strength of a 
given section of plate iron, as left, after 
punching, between two rivet holes, is 
actually less than the strength of an 
equal section of the same plate before 



61 



punching. In eight experiments, the 
highest strength of the plate experi- 
mented upon was 61,579 lbs., and the 
lowest 43,805 lbs., per sq. in., the aver- 
age of the whole being 52,486 lbs. per 
sq. in. But with the same plate, after 
punching, the strength per square inch 
of the metal left between the holes varied 
between only 45,743 lbs. and 36,606 lbs., 
the average of seven tests giving only 
41,590 lbs. per sq. in. of the remaining 
solid iron, against 52,486 lbs., the strength 
of the same section of the same iron be- 
fore punching. With this injury, there- 
fore, in punching the iron, by which 
even the remaining solid iron is weak- 
ened by more than one-fifth, the strength 
of an ordinary single riveted seam is, as 
was many years ago ascertained by Mr. 
Fairbairn, only 56 per cent., or a little 
more than one-half that of the same plate 
tested through solid iron away from the 
seam. Single riveting alone, therefore, 
destroys, upon the average, 44 per cent, 
of the strength of the weakest plate 



62 



worked into a steam-boiler.* In some 
cases, the injury by punching may be 
much greater than was apparent in Mr. 
Fairbairn's experiments. I have seen, in 
one of the most extensive engine works 
in France, punched plates of iron, T 6 oths 
in. thick, in which there were cracks 
from three consecutive rivet holes to the 
outer edge of the plate.f As sometimes 
made up (and in dealing with boiler- 
explosions it is our business to look for 
extreme cases), the plates are got together 
by the aid of "drifts," and the iron is 
under a greater or less initial strain be- 
fore steam is ever raised in the boiler. 

Apart from the quality of the mate- 
rials, and from the effects resulting from 
the ordinary processes of securing them 
together, the general construction of a 
steam-boiler greatly affects its strength. 
In Mr. Fairbairn's experiments upon the 
stayed sides of locomotive fire-boxes, a 
plate-iron box, made to represent the side 
of a strongly stayed fire-box, bore, in one 



* Manual, p. 117, § 50.— Ed. 
f Ibid. p. 123, § 51.— Ed. 



63 



case, the enormous pressure of 1,625 lbs., 
per sq. in. before yielding. The strength 
of the sides of a locomotive fire-box de- 
pends, however, almost entirely upon the 
stay-bolts alone, as without these the 
sides of the fire-box would be the weak- 
est parts of the whole boiler. Yet I have 
frequently found these stays (where made 
of wrought iron) to be as brittle, after a 
few years' use, as coarse cast iron. I 
have broken them off from the sides of 
old fire-boxes, sometimes with a blow no- 
harder than would be required to crack 
a peach-stone. The upper stay-bolts 
appear to suffer the most. Their deteri- 
oration, after long use, has been attrib- 
uted to slight but repeated bendings, 
caused by the expansion of the fire-box 
every time the fire is lighted, and its 
subsequent contraction when the boiler 
is again cooled. Upon this supposition, 
some locomotive makers turn these bolts 
to a smaller diameter in the middle of 
their lengths than at their ends, with the 
view of permitting a "spring" without, 



64 



short bending, under the alternating 
movements of the fire-box. 

Mr. Fairbairn's experiments upon the 
strength of iron tubes have, as is well 
known, disclosed most important facts 
bearing upon their relative resistance to 
internal and external pressure. Until 
the recent announcement of Mr. Fair- 
bairn's discovery that the resistance of 
metal tubes to collapse was, within cer- 
tain limits, inversely as their length, 
their strength, or, more properly speak- 
ing, their weakness, was generally un- 
known. One startling result, as ascer- 
tained from the experiments under 
notice, was, that, whilst the bursting 
pressure of a boiler 7 ft. in diameter, 30 
it. long, and composed of single-riveted 
-§ in. plates, of average quality, was 303 
lbs. per sq. in., the collapsing pressure of 
its 3-ft. internal plain flue of the same 
thickness of metal, was but little more 
than 87 lbs. per sq. in., or hardly more 
than one-fourth that required to burst 
the shell. * 

* Manual, p. 140, § 56. 



65 



Defects of Construction. — The steam 
domes of locomotive boilers are some- 
times of more than one-half the diameter 
of the barrel, which is consequently much 
weakened.* It has been observed that 
locomotive boilers frequently burst 
through the plates to which the dome is 
attached, or through the plates immedi- 
ately adjoining. Locomotive boilers, al- 
so, are occasionally, though not often, 
made of an oval section, their vertical 
diameter being 3 in. or 4 in. larger than 
the horizonal diameter. A large num- 
ber of the locomotives constructed by 
the late M. Camille Polonceau, at the 
Ivry workshops of the Paris and Orleans 
Eailway, have oval boilers of this kind. 
Although such boilers are unquestionably 
weaker than when made of a truly cylin- 
drical form, there are very few explosions 
upon the Orleans, or indeed upon any of 
the French lines. An engine exploded 
some two years ago at the Corbeil Station 
of the Orleans Eailway. 

The employment of angle-iron in the 

* Manual, p. 593, §285. 



66 



construction of many of the older locomo- 
tive boilers involved some danger, and it 
is doubtful if the real resistance of angle- 
iron to longitudinal cracking is known 
at all. In Messrs. Napier's experiments, 
last summer, four bars of Consett ship 
angle-iron bore from 43, 037 lbs. to 54,962 
lbs. per sq. in. when broken by a strain 
in the direction of their length. The 
process of manufacturing angle-iron tries 
it most severely, however (unless the iron 
be originally of the very best quality), by 
inducing incipient cracking along its 
length, giving it a reedy structure, and 
thus inviting the complete separation of 
one leaf from the other at the bend. 
Not a pound of angle-iron has been em- 
ployed for several years in the construc- 
tion of American locomotive boilers, and 
as far as I am aware the French locomo- 
tive makers have abandoned its use. All 
the angular junctions in the outer shells 
of American locomotive boilers are 
rounded with an easy curve of seldom 
less than 4 in. radius. The square cor- 
ners made in the inside fire-box plates, 



67 



which are almost always of iron, require 
the very best quality of metal of a thick- 
ness of not more than T 5 g- in., whilst the 
usual thickness is only J- in. I have fre- 
quently seen what was considered to be 
a good quality of f in. plate cracked 
completely in two under the attempt to 
bend it to a square corner. 

The defects originally existing in a 
plate of iron are occasionally discovered 
after its failure has produced a violent 
explosion. The freight engine Vulcan, 
employed upon the Buffalo and Erie 
Kailroad, IT. S., burst its boiler with ter- 
rific violence in August, 1856. Although 
the engine was one of three which had 
been built, as was believed with unusual 
care, one of the broken plates, afterwards 
recovered, exhibited a flaw 24 in. long. 
The plate which first gave way formed a 
part of the outer fire-box and extended 
to the dome, the 24 in. opening for 
which was an additional abstraction from 
the strength of the structure. The up- 
per part of,, the fire-box was blown com- 
pletely off to one side, and the engine 



68 



was thrown, bodily, 25 ft. to the other 
side, and into a ditch. 

The case of the engine Vulcan illus- 
trates that of many others where explo- 
sions have occurred in consequence of a 
congenital defect, after the boiler had 
been for a considerable time at work. It 
would be natural to ask why, if a boiler 
be originally defective, it does not ex- 
plode the first time it is brought under 
steam ? How can the final explosion be 
delayed one, two, or even ten years, when, 
all along, a hidden flaw, a broken rivet, 
or a rotten plate existed in the boiler ; 
and whilst explosion, therefore, must 
have been constantly impending under an 
almost perfect equilibrium between strain 
and resistance ? Does the strength of the 
boiler, after it has been completed, dete- 
riorate rapidly by use ? Mr. William 
Shaw, Jr., of the Tow-lane Ironworks,, 
Durham, wrote to " The Engineer" news- 
paper, under date of 15th December, 
1856, stating that, whilst he had 20 high- 
pressure boilers under his inspection, he 
had found fibrous iron, after a few years' 



69 



use, to become crystallized, and as brittle 
as blister steel. On the other hand, Mr. 
Samuel J. Hayes, formerly Master of 
Machinery of the Baltimore and Ohio 
Kailroad, U. S., and now holding a simi- 
lar appointment upon the Illinois Central 
Kailroad, at Chicago, 111., U. S., has in- 
formed me that he tested some of the 
plates of a boiler which exploded at Balti- 
more, in 1852, after 15 years' service, and 
that the iron bore an average tensile strain 
of 60,000 lbs. per sq. in. before yielding. 
It is doubtful if the iron in a steam-boiler 
alters its condition except by over-heat- 
ing; although certain parts of the boiler 
may sustain injury from alternate expan- 
sion and contraction. Mr. Frederick 
Braithwaite read a paper, some time ago, 
before the Institution of Civil Engineers,, 
upon the " Fatigue of Metals," in which 
paper iron was assume to lose its strength 
under long continued strain. I cannot 
enter here upon the conclusions of the 
paper in question, but I may refer to an 
experiment, made, I believe, by Mr. Fair- 
bairn, wherein a cast-iron column was 



70 



loaded with .97 of its estimated breaking 
weight, which weight was supported for 
six months, when the column broke.* 
It is evident enough that a steam-boiler, 
especially a locomotive boiler, is exposed 
to constant influences tending to weaken 
it ; and, apart from all reasoning under 
this head, the fact of the frequent quiet 
rupture of steam-boilers, sometimes after 
several years' steady work, is a sufficient 
proof that local defects, whether original 
or produced, may exist for a long time 
before the actual failure of the defective 
parts. 

Defects of Materials. — With regard gen- 
erally to failures resulting from an infe- 
rior quality of materials or workmanship, 
or ^from improper construction or man- 
agement, it may be said that whereas but 
one explosion occurred in the year 1859, 
among the 1,618 boilers under the care 
of the Manchester Boiler Association, no 
less than 14 boilers were found to be in a 
" dangerous" condition, and 100 in an 
"unsatisfactory" condition from the frac- 

* Manual, p. 74, § 35,— conclusive evidence on this point. 



71 



ture of plates ; at least one boiler out of 
every fifteen under inspection having ex- 
hibited an injury of that kind in a single 
year. But for the admirable system of 
boiler-inspection pursued in Manchester 
(and more recently adopted at Hudders- 
field), the larger number of these injuries 
would have remained undiscovered, and 
instead of one explosion there might have 
been twenty. 

Corrosion sometimes goes on entirely 
unsuspected. In a boiler which recently 
exploded at Tipton, considerable breadths 
of the iron were found to have been re- 
duced in thickness to -^ in. In the case 
of the explosion of a boiler at the Clyde 
grain mills, at Glasgow, in April, 1856, 
extensive breadths of the iron were said 
to have been reduced to the thickness of a 
sixpence ; and in the disastrous explosion 
which occurred in August of the same 
year, at Messrs. Warburton & Holker's, 
at Bury, the evidence showed that the 
bottom plates had been reduced for a 
greater or less width to only -^ in. in 
thickness. In the year 1859 there were 



72 



reported 44 cases of "dangerous/' and 
153 cases of "unsatisfactory" corrosion, 
among the 1,618 boilers under the inspec- 
tion of the Manchester Boiler Association. 
Thus there was nearly one case of corro- 
sion in every eight boilers, in a single 
year. 

All these facts, it will be observed, sup- 
port the probability of explosion at near- 
ly the ordinary working pressures. And, 
in the majority of cases, I believe it may 
be correctly assumed, in the absence of 
positive evidence to the contrary, that an 
exploded boiler, although to all appear- 
ance perfect up to the moment of rupture, 
contained some hidden defect. The fact 
of explosion, except under very peculiar 
circumstances, appears to be a better evi- 
dence of a defect in the boiler than of the 
previous existence, of anything like a cal- 
culated bursting pressure of steam ; such 
as 500 lbs. or 600 lbs. in a boiler made to 
work at 100 lbs. per sq. in.* 

* Manual, p. 642, § 295. This point is probably now be* 
yond question. — Ed. 



73 



If, however, boilers of the full calcu- 
lated strength have ever been burst by 
gradually accumulated pressure, it would 
be the easiest thing possible to prevent 
the recurrence of such disasters. If one 
one or two safety-valves are sufficient, 
under ordinary circumstances, to liberate 
the steam as fast as it may be generated 
in the boiler, three, four, or, certainly, 
half-a-dozen equally large safety-valves, 
all blowing off at just above the ordinary 
working pressure, and all acting indepen- 
dently of each other, would effectually 
prevent all chance of overpressure. If 
the explanation by overpressure, so per- 
sistently urged by Mr. Pairbairn, be the 
true explanation, boiler explosions may 
be entirely prevented, even where the at- 
tendants are guilty of the grossest care- 
lessness. For with a sufficient area of ef- 
fective safety-valve opening, it would be 
absolutely impossible, under the hardest 
firing, to raise the pressure 20 lbs. above 
the point at which the valves had been 
set to blow off. Safety-valves are simple, 
and comparatively inexpensive appliances, 



7'4 



and they should be so fitted so as to leave 
no doubt of their efficiency. Hawthorn's 
annular safety-valve, when its area is 
properly proportioned to the evaporative 
power of the boiler, renders any accumu- 
lation of pressure above the safe working 
limit quite impossible. Upon the loco- 
motives of some of the Austrian railways, 
Baillie's 12-in. safety-valves, held down 
by volute springs pressing directly upon 
the valve, are in use. In a trial made in 
Vienna, to ascertain the discharging 
power of this kind of valve, the fire in a 
locomotive fire-box was urged by a jet of 
steam in the chimney, the engine being 
at rest, and 80 cubic ft, or 2\ tons, of 
water were evaporated in one hour and 
discharged, in the form of steam, from the 
safety-valve. Although originally loaded 
to 64 lbs., the valve did not rise, during 
the experiment, above a point correspond- 
ing to a pressure of 76 lbs. per sq. in. 
The relief of pressure depends entirely 
upon the extent of safety-valve opening, 
supposing the valves to be in working or- 
der. Since the recent explosion of a lo- 



75 



comotive boiler on the Lewes branch of 
the Brighton Railway, Mr. Craven, the 
locomotive superintendent, has expressed 
his intention of applying three safety- 
valves, of the usual size, to each of his en- 
gines. Whilst it would be quite possible, 
with a boiler unprovided with safety- 
valves, or of which the valves were inop- 
erative, to produce an explosion by over- 
pressure, it would be equally impossible 
to do so when these outlets from the 
boiler were equal in discharging capacity 
to its evaporative power. The fact of 
explosion by sheer overpressure is a proof, 
simply, that the safety-valves were either 
inoperative or of insufficient size. 

Explosion at Ordinary Pressures. — If 
an iron cylinder be burst by hydrostatic 
pressure, the broken parts are not project- 
ed into the air. The pressure being re- 
lieved by the rupture of the iron, it ceases 
to act before the ruptured parts can ac- 
quire momentum. In the case of a loco- 
motive boiler bursting with only 75 cubic 
ft. of steam, of a pressure of 140 lbs. per 
square inch, there would be a considera- 



76 



ble expansive action after the plates were 
rent open. But this amount of steam, if 
expanded 685 cubic ft., equal to the vol- 
ume of a sphere 11 ft. in diameter, be- 
fore its pressure was reduced to that of 
the atmosphere, could hardly produce 
any very violent effects. So much of it 
would escape on the first opening of a 
seam of rivets, or other outlet, that a 
great part of the steam would be gone be- 
fore the parts of the boiler could be com- 
pletely separated. The range of action 
of this amount of steam would also be 
comparatively short, as it would have to 
expand only about nine-fold before all its 
expansive power would be gone. It is 
altogether improbable that, if steam only, 
of 140 lbs. to the square inch, were let 
into a close vessel calculated to burst at 
that pressure, the explosion would have 
the violence of a boiler-explosion under 
the usual circumstances. The laws of 
expansion of compressed air are nearly the 
same as those of steam, and vessels em- 
ployed in pneumatic apparatus are occa- 
sionally exploded, with an audible report 



77 



and a smart shock, it is true, but without 
that terrible energy in which steam-boiler 
explosions so much resemble the explosion 
of gunpowder. Steam cylinders sometimes 
fail; generally, however, from the con- 
cussion of the piston against water col- 
lected in the cylinder; but in such cases, 
with steam of nearly the full boiler pres- 
sure, and although the cylinder is formed 
of brittle cast iron, the broken parts are 
not projected violently away. In order 
to project bullets by steam, Jacob Per- 
kins employed pressures of from 300 lbs. 
to 950 lbs. per square inch, whilst one 
ounce of fine powder, to the detonation 
of which steam-boiler explosions are so 
frequently compared, will project a 24 
lbs. ball 300 yards; 225 yards being the 
least range, in such a proof, at which the 
powder is received into the service. But 
whatever may be the force of steam act- 
ing by itself, the sudden liberation of the 
heat, stored up, under pressure, in a 
considerable quantity of water, as in a 
boiler-explosion, would develop an addi- 
tional force. If, upon investigation, this 



force appears to be sufficient to account 
for the violent explosion of steam-boilers, 
after rupture has once commenced, in 
consequence of defective material or con- 
struction, and, as we may suppose, under 
an ordinary pressure, we shall not need 
to assume and to account for the exist- 
ence of extraordinary pressures like those 
with which Mr. Perkins experimented. 
If we consider heat as the source of 
power, and that the action of heat upon 
matter is always attended by the pro- 
duction of power, we shall be enabled to 
form a tolerable idea of the force con- 
cealed in a large body of highly heated 
water. The mechanical theory of heat 
has now attained such general accept- 
ance, that it is sufficient to bear in mind 
that the "unit of heat," or the total 
quantity of heat capable of raising the 
temperature of one English pound of 
water through one degree of the Fahren- 
heit scale — or, which is the same thing, 
that of 100 lbs. of water through .01 of 
a degree, or .01 lb. of water through 100 
deg. — that this quantity of heat, inde- 



79 



pendently of the medium through which 
it is exerted, possesses the same amount 
of power as would be required to raise 
772 English pounds through a space of 
one English foot, or 1 lb. through 772 
it., or 772 foot-pounds. If the addition 
of one degree of temperature to one 
pound of water be an addition of such a 
iorce, the addition of 100 deg. to 10,000 
lbs. of water is an addition of 1,000,000 
times the same force. In actual prac- 
tice, the combustion of a pound of coal 
imparts to the water in a steam-boiler 
&bout 10,000 units of heat, equal to the 
evaporation of 8 lbs. or 9 lbs. of water 
of ordinary temperature; and as in or- 
dinary working, and under many losses 
and disadvantages, a pound of coal exerts 
about one-fourth of one horse-power for 
one hour, or 15 horse-power for one min- 
ute, or 900 horse-power for one second, 
the heat stored up in 10,000 lbs. of water, 
in raising it through 100 deg. of tem- 
perature, is practically and actually equal 
to 25 horse-power exerted for one hour, 
or 1,500 horse-power exerted for one 



80 



minute, or 90,000 horse-power exerted 
for one second ! The heating of 10,000 
lbs. of water through 100 deg. of tem- 
perature represents but a small part of 
the heat contained in an ordinary steam- 
boiler; yet it practically requires the 
combustion of 100 lbs. of coal to effect 
it, and the heat imparted is equal to that 
expended in the conversion of about 870 
lbs. of water, of ordinary temperature, 
into steam. In a boiler explosion the 
contained heat is all disengaged in per- 
haps one or two seconds. 

Eecurring to the locomotive boiler, 
with 75 cubic ft. of water space and 75 
cubic ft. of steam-space, the correspond- 
ing weight of water would be 4,650 lbs., 
whilst the steam, even at 140 lbs. pres- 
sure, would weigh only 26 lbs. The 
temperature of this steam, however, 
which is the temperature also of the 
water from which it is formed, is 361 
deg., and the water is heated therefore 
149 deg. above the temperature at which 
it would produce steam, in the open air, 
of atmospheric pressure. Water could 



81 



only be heated to this temperature by 
being confined under a corresponding 
pressure, and if, when the water has 
been so heated, the pressure is removed, 
the water cannot remain in its original 
condition as water merely, but a part of 
it becomes immediately converted into 
steam. 4,650 lbs. of water, heated to 361 
deg., contains as much heat, or as many 
'"units of heat/' over and above the heat 
at which it gives off steam of atmospheric 
pressure, as are contained in 577 lbs. of 
steam of a total temperature of 1,200 
deg. It is fair to presume, therefore, 
that upon the sudden liberation of the 
pressure under which 4,650 lbs. of water 
liad been heated to 361 deg., about 577 
lbs. of it would be immediately converted 
into steam. This quantity is more than 
twenty-two times greater than that of 
the steam originally contained in 75 
cubic ft. of space, and at a pressure of 
140 lbs. per sq. in. 

If we suppose a considerable rupture 
of any part of the boiler, anywhere 
above the water-line, the steam already 



82 



formed would rush out with a velocity 
at first of about 2,000 ft. per second. 
Before the heat, contained in the water, 
could so far overcome the inertia of the- 
water as to disengage additional steam, 
the upper part, or steam-space of the 
boiler, might be nearly emptied. The- 
steam which would inevitably rise from 
the water would thus strike at a very 
great velocity upon the upper part of 
the boiler, and no doubt, as Mr. D. K. 
Clark has suggested, in a communicatiou 
to the " Mechanics' Magazine/' of 10th 
February, 1860, the steam carries a 
great quantity of water with it. In some' 
of the earlier locomotives, having a de- 
ficiency of steam room, the partial re- 
moval of the pressure from the water, by 
opening the regulator or " throttle/'' 
was attended by a rise of the water to* 
the extent of from 8 to 10 in. But 
whilst this result attended the removal 
of perhaps -^ of the superincumbent, 
pressure, its sudden and entire removal 
would cause a tremendous blow to be 
discharged — whether by the steam alone 



83 



or by the combined steam and water — 
upon the sides of the boiler, sufficient, 
no doubt, not only to extend the rup- 
ture already existing, but to completely 
rend the boiler in two or more parts. 
In the case of the explosion at Birming- 
ham, on the 5th March, 1857, of engine 
Ho, 175, belonging to the Midland 
Kailway Company, the boiler was broken 
into 17 pieces. These effects would 
follow when the boiler had ruptured, 
in consequence of some defect in its 
structure, under a moderate working 
pressure, as well as under such immense 
pressures as are commonly assumed in 
cases of violent explosion. There is 
reason to believe that steam alone, strik- 
ing at a great velocity upon a solid sur- 
face, can discharge a violent blow, in ad- 
dition to whatever effect it may produce 
by its pressure when at rest. Mr. D. K 
Clark has mentioned to me that where 
he had applied an indicator to a locomo- 
tive cylinder in which there was little or 
no compression, the sudden admission of 
steam through a large steam-port not 



84 



only carried the pencil of the indicator 
above the point corresponding with the 
highest pressure in the steam-chest, but 
a positive blow was discharged upon the 
finger when placed upon the pencil- 
holder of the indicator. The same 
gentleman has mentioned to me also a 
fact which has been observed in the 
working of the Cornish engines, where 
steam of moderately high pressure is ad- 
mitted into large cylinders, sometimes 
100 in. in diameter. The cylinder covers 
are found to " spring" with each admis- 
sion of steam, indicating a smart shock 
in addition to the pressure, which, after 
the piston has commenced its stroke, 
can only act statically upon the cylinder 
cover. Some years ago, and before the 
days of steam-gauges, one Signor Morosi 
maintained the extraordinary opinion 
that on the stoppage of the piston at 
each end of its stroke, the whole force 
of the steam was so violently stopped in 
its motion as to strike back forcibly into 
the boiler, like the water in the hy- 
draulic ram, impinging as would a solid 



85 



body upon the boiler plates.* The per- 
cussive action of steam is certainly not 
so great as this; for it is only when 
steam strikes through an intervening 
space upon an unyielding surface and 
with a velocity of several hundred feet 
per second, that it can be considered to 
act with any amount of percussion worth 
mentioning, and not when reacting (if 
indeed it did react) against a large body 
of steam within a boiler, and at the slow 
speed of a steam-engine piston, gradually 
extinguished as its motion is at each 
end of its stroke. And, of course, upon 
Signor Morosi's notion, the boiler should 
explode, if at all, when the engine makes 
its first stroke. In practice, the steam- 
gauge, which has since come into general 
use, is found to indicate a constant 
pressure without reference to the chang- 
ing of the strokes of the piston, except- 
ing where the steam-room of the boiler 
is very much too small. 

But the momentum of the combined 

* Dr. Alban on the "High-pressure Steam-engine," 
translated by Wm. Pole (p. 27). London: Weale, 1848. 



S6 



steam and water, discharged, as Mr. 

Clark lias suggested, in his communica- 
tion already referred to,* would prob- 
ably be sufficient to overcome the resist- 
ance of the material of the boiler and to 
rend it open, not only along seams of 

* The following is a copy of Mr. Clark's letter: 

TO THE EDITORS OF THE " MECHANICS" MAGAZINE." 

11 Adams Street, Adelplii. London, Feb. 9. 1S60. 

Gentlemen. — I have within the last few months given 
some attention to the subject of boiler explosions— their 
causes, and their rationale. I observe, in the discus- 
sions that have appeared in contemporary papers, that 
the percussive force of the steam suddenly disengaged 
from the heated water in a boiler, acting against the 
material of the boiler, is adduced in explanation, and as 
the cause of the peculiar violence of the result of explo- 
sion. 

Now. gentlemen, a little calculation would show that 
the percussive force of steam is not capable of causing 
such destructive results as are occasionally produced; 
and I beg leave to suggest that the sudden dispersion 
and projection of the water in the boiler against the 
bounding surfaces of the boiler is the great cause of the 
violence of the results: the dispersion being caused by 
the momentary generation of steam throughout the 
mass of the water, and its efforts to escape. It carries 
the water before it. and the combined momentum of 
the steam and the water carries them like shot through 
and amongst the bounding surfaces, and deforms or 
shatters them in a manner not to be accounted for by 
simple overpressure or by simple momentum of steam. 
Your obedient servant. 
D. K. Clark. 



87 



rivets, but, as is often the case, through 
solid iron of the strongest quality. The 
velocity with which the steam and water 
would strike would depend upon the 
extent to which the steam-space of the 
boiler had been emptied of steam, before 
the inertia of the boiler had been over- 
come by its contained heat. The water 
carried with the steam would not retain 
its ordinary condition as a liquid, but, 
being completely pervaded by nascent 
steam, would have the character of an 
expansive body of more or less elasticity. 
The destructive effects produced by the 
inevitable concussion of such a body 
upon the upper portion of a cylindrical 
boiler (and the water being originally in 
the bottom of the boiler would only 
strike upwards) cannot be estimated 
therefore by multiplying its weight, as 
if it were a solid body, into the veloc- 
ity assumed to be acquired in the 
distance through which it would be 
projected against the iron shell of the 
boiler. It is very likely that the mo- 
mentum of the steam and water is ex- 



pended mainly in breaking the plates, 
especially through strong solid iron, and 
that if no additional force were after- 
wards brought into play the ruptured 
parts of the boiler would drop to the 
ground, or, at the most, be projected 
.only to a short distance. But at the 
moment when the steam and water rise 
to the upper part of the boiler, and, in- 
deed, until a large outlet is provided (as 
when, perhaps, the boiler is forced com- 
pletely open), the quantity of steam dis- 
engaged will be very small indeed ; not 
greater than the quantity originally con- 
tained in the steam-space of the boiler. 
Whatever may be the quantity of heat in 
the water, it cannot convert any portion 
of the water into steam of a greater pres- 
sure than that under which only the 
water was originally heated ; that is to 
say, water heated, for instance, to 361 
deg. cannot at that heat produce steam, 
spontaneously, of a greater pressure 
than 140 lbs. per sq. in. It is after the 
b>oiler has been rent completely open, 
and after its separated portions have, 



89 



perhaps, been started upon different 
courses through the air, that the great 
disengagement of steam from the heated 
water must take place. This phenome- 
non can only occur after the boiler has 
heen rent completely open, or, at least, 
when the water is no longer confined 
within its original limits, because the 
original capacity of the boiler would be 
insufficient for the disengagement of the 
steam, which, as it can never rise much 
above its original density, can only dis- 
engage itself upon the expansion of the 
water in which it was] previously con- 
fined. Assuming 577 lbs., or 9.25 cubic 
ft., of the water contained in the loco- 
motive boiler, already described, to be 
converted into steam of atmospheric 
pressure, it would form 15,188 cubic ft. 
of steam, equal to the volume of a sphere 
of 31 ft. diameter ; and until the dis- 
engaged steam had expanded to this 
volume at least, the parts of the ex- 
ploded boiler would be within the range 
of explosive action. Under the velocity 
with which, as in the explosion of large 



90 



boilers,, more than one ton of elastic 
yapor would discharge itself into the air, 
the projection of fragments of the boiler, 
weighing 5 cwt., to a distance of 350 
yards, as in the explosion at Wharton 
Colliery, near Chesterfield, in June, 
1856, is not perhaps anything to be won- 
dered at. 

Under the foregoing explanation of 
boiler explosions their results are pro- 
duced by a series of consecutive opera- 
tions, the first of which is the rupture of 
some portion, generally a defective por- 
tion, of the shell of the boiler ; the rup- 
ture, unless it be of considerable extent, 
occurring generally — in cases of violent 
explosion — above the water-line. If a 
narrow rent take place in the bottom of 
the boilei the pressure upon the water 
will not be removed until the water falls 
to the level of the discharging opening ; 
and hence, as the water is not likely to 
escape with very great rapidity, no per- 
cussive action will occur within the 
boiler, from steam, either disengaged 
by itself, or in combination with waterj 



91 



and the steam which, is disengaged, 
from the escaping water will be already 
out of the boiler at the moment of its 
disengagement. 

The distinct and consecutive opera- 
tions into which a boiler explosion, al- 
though practically instantaneous, may 
probably be resolved, are, therefore, 
these : — ■ 

1. The rupture, under hardly if any 
more than the ordinary working pres- 
sure of a defective portion of the shell of 
the boiler ; a portion not much, if at all, 
below the water-line. 

2. The escape of the free steam from 
the steam-chamber, and the consequent 
removal of a considerable part of the 
pressure upon the water, before its con- 
tained heat can overcome its inertia and 
permit the disengagement of additional 
steam. 

3. The projection of steam, combined 
as it necessarily must be with the water, 
with great velocity and through a 
greater or less space, upon the upper 
sides of the shell of the boiler, which is 



92 



thus forced completely open, and per- 
haps broken in pieces. 

4. The subsequent disengagement of a 
large quantity of steam from the heated 
water now no longer confined within the 
boiler, and the consequent projection of 
the already separated parts of the boiler 
to a greater or less distance. 

The rapidity of the escape of the 
steam, through a narrow opening, may 
be understood practically by observing 
an indicator diagram, taken from a loco- 
motive cylinder when the engine is run- 
ning at a high speed. The , driving- 
wheels, at high velocities, revolve be- 
tween four and five times every second, 
and each cylinder must exhaust twice at 
each revolution, or perhaps ten times in 
1 sec. An examination of the indicator 
diagram will show, moreover, that the 
actual exhaustion, at each half-revolu- 
tion of the wheels, does not occupy 
much, if any, above one-fourth of the 
time in which such half-revolution is 
made — each complete exhaustion of a 
cylinder-full of high-pressure steam oc- 



93 



cupying, therefore, but about one- 
fortieth of 1 sec., notwithstanding the 
length and tortuous character of the ex- 
haust passages, and the comparatively 
gradual opening of the valve. 

The force with which steam in motion 
will take up and carry water with it may 
be seen in the " Automatic Injector/" or 
feed- water apparatus, of M. Henri Gif- 
fard, as made by M. Flaud, of the Eue 
Jean Goujon, Paris, and more recently, 
by Messrs. Sharp, Stewart & Co., of 
Manchester, and the Eogers Locomotive 
and Machine Company, of Paterson, TJ. 
S. In this apparatus, a jet of steam dis- 
charged through a conical nozzle, draws 
up a considerable body of feed-water 
and impels it, first for a short distance 
through the open air, and thence, 
through a valve, into the same boiler 
from which the steam was originally 
taken. The under side of the clack 
valve— or so much of its under side as 
receives the impact of the water before 
the valve r* raised from its seat — has, of 
course, less area than the upper side, 



94 



on which the pressure within the boiler 
is exerted. Hence, to force water into 
the boiler against a pressure of, perhaps, 
120 lbs. per sq. in., a pressure of, prob- 
ably, at least 175 lbs. per sq. in. of the 
under side of the valve, has to be first 
exerted by the jet of combined steam 
and water. The jet at the same time is 
very small, and must move with consid- 
erable friction, which, therefore, by so 
much diminishes its original force of 
motion. 

Where, therefore, a rupture is not at- 
tended by explosion, it is to be presumed 
either that the relief of pressure is not so 
sudden as to induce percussive action by 
the steam spontaneously generated, or 
else that, even with the partial or total 
removal of the pressure, the quantity of 
heat stored up in the water is insufficient 
to complete the explosion. If a very 
small crack occur above the water-line, 
or if a considerable aperture be very 
gradually opened, the removal of the 
pressure upon the heated water will be so 
gradual that no violent percussive action 



95 



may be induced, and, as has been already 
observed, if the rupture occur below the 
water-line, the pressure upon the water 
may not be removed until it has been 
almost wholly discharged from the boiler. 
The dome covers of locomotive boilers 
are sometimes blown off without ex- 
plosion, but here it is probable that the 
fastening bolts do not all give way at 
once, and that the opening for escape 
enlarges gradually before the cover is 
forced completely off. In 1853, the 
boiler of locomotive No. 4 of the New 
York and New Haven Kailroad, ruptured 
along the junction of the barrel of the 
boiler with the dome. The steam was 
lost and the train detained, but no 
further damage was done. In the winter 
of 1856-7 the boiler of one of the loco- 
motives of the New York and Harlem 
Railroad ruptured through the under- 
side of the cylindrical barrel, the results 
being similar to those just mentioned. 

Another case, which came under my 
own observation, was that of a locomo- 
tive fire-box, which was ruptured at the 



96 



Dunkirk shops of the New York and 
Erie Kailroad. One seam of rivets had 
opened, on the outside fire-box, 1 in. in 
width, and perhaps 2 ft. in height. The 
further opening of the seam had been 
prevented by the framing of the engine, 
which extended along the side of the 
fire-box. No violent consequences at- 
tended this rupture. In his last report, 
H. W. Harman, C. E., Chief Inspector 
to the Manchester Boiler Association, 
states that in one case which occurred 
under his inspection, an oval flue col- 
lapsed with complete rupture of the 
plates, in consequence of the gradual 
admission of steam through the stop- 
yalve of an adjoining boiler, and of 
higher pressure than the flue was capable 
of sustaining. "But," adds Mr. Har- 
man, st no explosion occurred; it came 
quietly down, and the contents were 
discharged into the boiler house without 
any report whatever; and in another 
case arising from deficiency of water, the 
plates became overheated and flattened 
sufficiently to derange the seams, and a 



97 



portion of the water escaped, also with- 
out concussion." 

As already observed, the percussive 
action exerted by the combined steam 
and water, upon the sudden removal of 
the pressure, must be exerted mainly up- 
wards, and probably the larger number 
of exploded boilers first give way in the 
upper part of the barrel. Comparatively 
few locomotive boilers ever leave the rails 
when they explode, unless the roof of 
the inside fire-box is crushed down. In 
^February, 1849, the boiler of a locomo- 
tive employed on the Boston and Provi- 
dence Railroad, United States, exploded 
with great violence whilst the engine 
was running with its train, and just after 
the steam had been shut off in approach- 
ing the Canton station. The engine did 
not leave the rails, but ran some distance 
after the explosion. The explosion of 
engine No. 58, upon the New York and 
Erie Railroad, in the summer of 1853, 
was attended with much the same results. 
The engine Wauregan, the explosion of 
which has been already mentioned, was 



not moved from the rails. Locomotive 
]STo. 77, of the New York Central Kail- 
road, exploded in the winter of 1856-7, 
whilst running with a train, and just 
after the steam had been shut off. The 
engine did not leave the rails. Much of 
the iron in the barrel of the boiler was 
nearly as brittle as cast iron. Engine 
No. 23, of the Baltimore and Ohio Kail- 
road, exploded violently at about the 
same time and in nearly the same man- 
ner. The engine of which the boiler 
burst in Messrs. Sharp, Stewart & Co/s 
Works, in the summer of 1858, was not 
thrown from the rails, although the 
explosion was one of terrific violence. 
Nearly all of these explosions occurred 
in the waist of the boiler, towards the 
smoke-box end. In but one of the six 
explosions just mentioned was there any 
evidence of the overheating of any por- 
tion of the boiler. The tubes were in 
nearly every case bulged outwards be- 
yond the original diameter of the boiler, 
showing that in the disengagement of 
steam from the water contained among 



99 



them a considerable outward pressure 
had been exerted; although the closeness 
of the tubes, and the consequent want 
of any clear space through which the dis- 
engaged steam could strike, precluded 
the supposition of percussive action, 
which, indeed, had it occurred, would 
have broken the tubes to pieces, and 
driven them in every direction, instead 
of bending them merely. 

In the case of the locomotive Irk, 
which exploded in the Manchester engine- 
shed of the Lancashire and Yorkshire 
Eailway, in February, 1845; in that of 
the explosion at Eogers, Ketchurn & 
Grosvenor's in May, 1851; in that of 
engine No. 100, which exploded on the 
Isew York and Erie Eailroad, in 1852 I 
believe, and in the case of the explosion 
of an agricultural engine, at Lewes, 
Sussex, in September last, the roof of 
the fire-box was in each case forced down- 
wards, the steam discharging below, and 
the engine was, in every instance, thrown 
into the air. Considering that the or- 
dinary pressure upon the crown-plate of 



100 

a, locomotive* fire-box is from 80 to 150 
tons, there is no difficulty in accounting 
for these results, after the plate has once 
gone down. 

The boiler explosion which occurred 
at Messrs. Warburton & Holker's Works 
near Bury, on the 15th of August, 1856, 
was believed to have commenced in 
the bottom of the boiler. An extensive 
crack was known to have existed there, 
and it had been twice patched, notwith- 
standing which, a considerable breadth of 
iron was afterwards found to have been 
reduced to a thickness of only -^ in. But 
as the boiler was 36 ft. 6 in. long, and 
no less than 9 ft. 1 in. (109 in.) in 
diameter, and as it was worked, after its 
f th in. plates had been 11 years in use, 
at a pressure of 40 lbs. per sq. in., 
the final rupture* of the bottom was 
in all probability instantaneous for a 
great length, especially as the boiler 
was riveted up with continuous seams, 
or seams which did not break joints 
with each other! This huge bomb-shell 
was said to have contained 56 tons of 



101 

water at the moment of explosion ; which, 
quantity heated to 287 cleg., correspond- 
ing to the pressure at which the explo- 
sion took place, would have given off at 
least 3-J- tons of steam ! It has, indeed, 
been assumed, that in many cases of ex- 
plosion, all the water previously con- 
tained in the boiler is converted into 
steam. Mr. Edward Woods once men- 
tioned, at the Institution of Civil Engi- 
neers, an instance which came under his 
observation, in 1855 I believe, and where, 
after a locomotive boiler had burst, the 
whole of the water was found to have 
completely disappeared. Mr. Yaughan 
Pendred, of Dublin, has informed me 
that he observed a similar result after he 
had exploded a small boiler, well supplied 
with water, for the purpose of experi- 
ment. He had erected a fence of boards 
about the place where the boiler was 
allowed to burst, but on going to the spot 
immediately afterwards no traces of water 
€ould be seen. I cannot adopt the idea, 
however, that all the water, heated, 
probably, to less than 400 deg., is actu- 



102 

ally converted into steam. It is, no 
doubt, dispersed in a state of minute 
division and to a great distance ; but the 
greater portion of it must still maintain 
its existence as water, since its contained 
beat is insufficient to convert it into 
steam. But there can be no doubt of 
the sudden generation of steam and pro- 
jection of the water, when the pressure, 
under which water has been heated, is 
suddenly removed, and it is probable that 
water, heated in the open air to 212 deg., 
would be sufficient to produce violent 
explosion if suddenly placed in a vacuous 
space, corresponding, in its proportions 
to the contained water, to an ordinary 
boiler. A boiler, 24 ft. long and 10 ft. 
in diameter, burst with great violence on 
the 9th December, 1856, at Messrs. Cress- 
well & Son's ironworks, at Tipton. In 
this case it was observed that the floor of 
the boiler house, immediately after the 
explosion, was covered with water, and 
this fact was taken as evidence of a suf- 
ficiency of water in the boiler. The 
boiler had been in use for some 18 years, 



103 

but its plates had retained an average 
thickness of § in. Had the plates been 
of good quality originally,, and had they 
suffered no deterioration in the long 
time during which the boiler had been 
worked, the bursting pressure would have 
been 167 lbs. per sq. in. The explosion 
of the boiler was attributed to overpres- 
sure, although the regular working pres- 
sure was but 17 lbs. per sq. in. 

The idea has been already suggested 
that heated water, if suddenly placed in 
a vacuous space, would disengage steam 
with great violence. The result would 
be necessarily the same whether the 
pressure, under which the water had 
been heated, were suddenly removed by 
exhaustion or by condensation. And if 
it were purposely sought to condense the 
steam in the upper part of a boiler, this 
could be effected with lightning-like 
rapidity. When steam of considerable 
pressure is discharged into a condenser 
of suitable capacity, the condensation is 
so instantaneous that the index of the 
vacuum gauge does not move at all. 



104 

Even in surface condensers, in which 
the steam, is let in upon several hundred 
square feet of tubular surfaces, kept cool 
by a constant circulation of water, the 
same instantaneous action takes place. 
If, therefore, a sufficient quantity of cold 
water — or water considerably below the 
boiling point corresponding to the pres- 
sure — were suddenly thrown up among 
the steam, its condensation would as 
suddenly take place. An instant can 
thus be conceived in which no pressure 
would exist upon the water, which, as 
soon as its inertia could be overcome by 
its contained heat, would, therefore, be 
thrown violently against the upper part 
of the boiler, causing its explosion in the 
manner already explained. Whether, in 
the practical working of a steam-boiler,, 
circumstances ever arise in which such 
condensation could occur, is a matter of 
conjecture. In locomotive engines, for 
example, the feed water is commonly 
pumped into the boiler at two points on 
either side, a little below the ordinary 
water level. With both pumps on, from 



105 

100 to 175 cubic inches of water are 
pumped in at each revolution of the 
driving wheels ; and at a speed of even 
30 miles an hour, from 10 to 15 cubic 
feet, or from 600 lbs. to 1,000 lbs. of water 
would be pumped in every minute. If 
this water were pumped in at the water 
level, it might not, obstructed as its 
descent would be by the closely packed 
tubes, mix with the water already in the 
boiler, until after some minutes ; espe- 
cially if the engine were running by 
momentum only, after the steam had 
been shut off, and when, therefore, but 
very little steam would be in process of 
generation, and when the circulation of 
the water would be consequently sluggish. 
If a stratum of cool water were to ac- 
cumulate over the tubes, it would require 
a long time to heat it, especially if the 
draught had been stopped by shutting 
off the steam. Indeed 10 cubic feet of 
feed water, without circulation and con- 
sequent mixture with the hot water 
already in the boiler, would not, «ven 
when in contact with the heating sur- 



106 

faces, become heated to the boiling point 
in much less than a quarter of an hour. 
As long, however, as this water remained 
quiescent, the steam accumulated over it 
would be condensed only very slowly. 
But if, as by suddenly turning the steam 
again into the cylinders, the diminution 
of pressure, and consequent rise of water, 
were such as to throw up a considerable 
quantity of it into the steam-chamber, 
the free steam might be instantly con- 
densed, and, in such case, the reasoning 
already adopted would support the prob- 
ability of instant explosion. In this 
case, the actual occurrence of which is 
not, perhaps, impossible, it would not be 
necessary to assume the existence of any 
defect in the boiler ; for, when the water 
once struck violently, the soundest iron 
would probably be broken, and the strong- 
est workmanship destroyed. 

Locomotive boilers often burst in the 
plates next to the smoke-box, beyond the 
reach of the fire, and where the boiler is 
believed to be stronger than about the 
fire-box. As has been observed, the dome, 



107 

if it open from the ring of plates in 
question, weakens it materially ; but 
explosions have occasionally occurred in 
this part of a boiler, either having no 
dome, or having one only over the fire- 
box. A fact which was some time 
since communicated to me by George 
S. Griggs, Esq., Locomotive Superin- 
tendent of the Boston and Providence 
Eailroad, U. S., may assist in explain- 
ing this somewhat anomalous mode of 
explosion. In one or two cases of loco- 
motive boiler explosions, Mr. Griggs 
found, upon examination, that whilst 
none of the upper tubes had been burnt, 
others, lower down, exhibited unmis- 
takable indications of having been 
smartly scorched ; the solder used in 
brazing being more or less melted. The 
tubes being closely packed in the boiler, 
it appeared that the heat passing 
through them had dispersed the water 
from their sides; the water level being 
but about 15 in. above, and the conse- 
quent pressure of water, resulting from 
this amount of "head," being only 



108 

about one-half pound per square inch to 
overcome the violent disengagement of 
steam in the restricted passages below. 
The admission of water through the 
" check-valve" of the pump would sud- 
denly cool the parts of the boiler with 
which it came first in contact, and 
would, no doubt, cause the partial re- 
turn of the water to the surfaces from 
which it had been expelled. Sufficient 
steam might be thus disengaged, by 2 
cwt. or 3 cwt. of highly heated copper or 
brass tubes, to exert a sudden and pow- 
erful strain upon the surrounding parts. 
Mr. 0. Wye Williams has mentioned, in 
his work on the Combustion of Coal, a 
circumstance similar to that observed by 
Mr. Griggs. In one of the deep and 
narrow water-spaces of the boilers of the 
Great Liverpool steamship, the engineer 
found, on the first trip of that vessel to 
New York, in 1842, that the side plates 
were constantly giving way. On tap- 
ping a gauge-cock into the space, several 
feet below the water level, only steam 
was discharged, although the water was, 



109 

at the same time, standing several feet 
above. In nearly all American and in 
the majority of French locomotives, of 
recent construction, the tubes are dis- 
posed in vertical rows, in order to assist 
the circulation of the water. Mr. Griggs 
has assured me that some of his engines, 
with closely packed tubes, have actually 
made steam more freely after he had 
plugged the ends of ten or a dozen 
tubes, one over the other, in the middle 
of the boiler. As long as the water was 
not in complete contact with these tubes, 
the heat which before passed through 
them was to a greater or less extent lost. 
I have myself observed that a class of 
locomotives having 130 tubes, 2 in. in 
diameter, made steam more freely than 
another class, in all respects the same, 
with the exception of having 144 tubes, 
If in. in diameter, although the actual 
extent of heating surface was hardly 
more in the former than in the latter 
case. 

The quantity of water contained in 
steam-boilers of a given length, and the 



110 

consequent quantity of explosive matter 
which they contain under any given 
pressure, is, practically, as the square of 
their diameters; and although different 
boilers, of the same materials and work- 
manship, are believed to be equally 
strong to resist rupture when the thick- 
ness of their plates bears the same ratio 
in every case to their diameter, the real 
danger, which ensues after rupture has 
actually commenced, may be estimated, 
so to speak, as the square of their diame- 
ter and directly as their length, or, in 
other words, as directly proportional to 
the quantity of water which they contain 
at any given temperature. Although 
locomotive boilers, perhaps, sustain a 
greater proportionate strain than ordi- 
nary land boilers, and are, for that 
reason, somewhat more liable to explo- 
sion, the effects resulting from their ex- 
plosion are seldom anything like those 
which attend the destruction of large 
land boilers, even when working at very 
moderate pressures. The Great Eastern 
casing, which exploded with great vio- 



Ill 

lence on the trial trip last September, 
was no more than a large boiler, 7 ft. in 
diameter, with an internal flue of 6 ft. 
diameter, and which was, practically, un- 
stayed. The collapse of this flue, under 
a moderate pressure, and the consequent 
liberation of the heat contained in the 
hot feed-water, of which the casing was 
made to hold 11 tons, was sufficient, 
upon the explanation herein advanced, 
to account for the disastrous character 
of the explosion. 

I think there can be no doubt that a 
consideration of the expansive power of 
a large body of highly heated water, act- 
ing under the instigation of a sudden 
removal of the pressure (with the aid of 
which only it was possible to heat it 
above 212 deg.), is capable of clearing 
up much of the mystery which has for 
so long a time enshrouded the subject of 
Boiler Explosions. Such a considera- 
tion leads to a comprehensible and ration- 
al explanation of these disasters; one 
which, upon a rigid process of reason- 
ing, appears sufficient to account for all 



112 

or nearly all cases of the kind. Whilst 
the present essay may serve to commend 
this explanation to engineers and to the 
public generally, I hope it may also 
hasten the adoption of smaller and more 
numerous water-spaces in steam-boilers, 
as in the water-tube arrangement, which, 
with pure water, is, in my opinion, the 
safest, most efficient, and most economi- 
cal yet devsed for the generation of 
steam. But, above all else, public safety 
requires the frequent and systematic ex- 
amination of all steam-boilers, so that, 
as under the system of inspection which 
is in operation with such excellent re- 
sults at Manchester and Huddersfield, 
defects may be discovered and remedied, 
in most cases before actual danger has 
been incurred. 

All our knowledge of boiler explosions 
goes to show that, however possible it 
may be to accumulate an excessive pres- 
sure within a boiler, the actual explosion 
results, in the majority of cases, from 
some defect, either original or produced, 
and either visible or concealed, in the 



113 

materials, workmanship, or construction 
of the boiler. Probably not much more 
than one per cent, of all the steam 
boilers made ever explode at all, and the 
results of systematic inspection show that 
a far higher percentage of the whole 
number of boilers are constantly in a 
condition inviting explosion, and from 
causes which a general examination would 
not only disclose, but of which it would 
also insure the removal. 



I 




THE VAN NOSTRAND SCIENCE SEEI 



No 
No 
No 


. 44. 

. 45. 

46. 


No 


47. 


No 


48.- 


No. 


49.- 


No 


50.- 


No. 


51.- 


No. 


52.- 


No. 


53.- 


No. 


54.- 


No. 
No. 


55.- 
56.- 


No 


57.- 


No. 


58.- 


No. 


59.- 


No. 


60.- 


No. 


61.- 


No. 


62- 


No. 


63.- 


No. 
No. 


64.- 
65.- 


No. 


66.- 


No. 
No. 
No. 
No. 
No. 


67.- 
68- 
69.- 
70.- 
71.- 



-TURBINE WHEELS. By Prof. W. P. Tnro 
-THERMODYNAMICS. By Prof H. T. Edd 
-ICE-MAKING MACHINES. From the F- 
M. Le Doux. 

—LINKAGES ; the Different Forms and Uses 

ticulated Links. By J. D. C. De Roos. 
-THEORY OF SOLID AND BRACED ARCH 

Wm. Cain, C. E. 
-ON THE MOTION OF A SOLID IN A FLU 

Thomas Craig, Ph. D. 
-DWELLING HOUSES • their Sanitary Consi 

and Arrangements. By Prof. Wm. H. Cor 
-THE TELESCOPE: Its Construction, & 

Thomas Nolan. 
-IMAGINARY QUANTITIES. Translated f 

French of M. Argand. By Prof. Hardy. 
-INDUCTION COILS : How Made and Hoy 

3d Edition. 
-KINEMATICS OF MACHINERY. By Pro 

nedy. With an introduction by Prof. Thu 
-SEWER GASES. By A. De Varona. 
-THE AC TUAL LATERAL PRESSURE OF ] 

WORK. By Benj. Baker, M. Inst. C. E. 
-INCANDESCENT ELECTRIC LIGHTS, By 

Th. Du Moncel and Wm. Henry Preece. 2d 
-THE VENTILATION OF COAL MINES. 

Fairley, M. E., F. S. S. 
-RAILROAD ECONOMICS ; or Notes, wit 

ments. By S. W. Robinson, C. E. 
-STRENGTH OF WROUGHT IRON BRIDG] 

BERS. By S. W Robinson, C. E. 
-POTABLE WATER, and the Different Met 

Detecting Impurities. ByChas. W. Folk; 
-THE THEORY OF THE GAS ENGINE. By 

Clerk. 
-HOUSE DRAINAGE AND SANITARY P 

ING. By W. P. Gerhard. 2d Edition. 
-ELECTRO-MAGNETS . By Th . du Moncel . 
-POCKET LOGARITHMS TO FOUR PLAC 

DECIMALS. 
-DYNAMO-ELECTRIC MACHINERY. By S 

P. Thompson. 
-HYDRAULIC TABLES. By P. J. Flynn, C. 
-STEAM. HEATING. By Robert Briggs. 
-CHEMICAL PROBLEMS. By Prof. Foye. 
- EXPLOSIVE MATERIALS. By M. P. E. Bei 
DYNAMIC ELECTRICITY By John Hop, 

J. A. Schoolbred and R. E. Day. 



1 



THE VAN NOSIRAND SCIENCE SERIES. 



No. 72.—' 



No. 


73 


No. 


74 


No. 


75. 


No. 


76. 


No. 


77 


No. 


78 


No. 


79. 


No. 


80 


No. 


81 


No. 


82 


No. 


83. 


No. 


84. 



No. 85. 
No. 86. 

No. 87. 



No. 


88.- 


No. 


89. 


No. 


90- 


No. 


91. 


K). 


92.- 


tfo. 


93. 


No. 


94. 


7n t o. 


95. 



TOPOGRAPICAL SURVEYING. By Geo. J. Specht, 
Prof. AS. Hardy, John B. McMaster and H F. 
Walling. 

-SYMBOLIC ALGEBRA ; or The Algebra of Algebraic 
Numbers. By Prof. W. Cain. 

—TESTING MACHINES; their History, Construction 
and Use By Arthur V. Abbott. 

-RECENT PROGRESS IN DYNAMO-ELECTRIC MA- 
CHINES Being a Supplement to Dynamo- Elec- 
tric Machinery. By Prof. SilvanusP Thompson. 

-MODERN REPRODUCTIVE GRAPHIC PRO- 
CESSES. By Lt. Jas. S. Pettit, U.S.A. 

-STADIA SURVEYING. The Theory of Stadia 
Measurements . By Arthur Winslow . 

-THE STEAM ENGINE INDICATOR, and its Use. 
By W. B Le Van. 

-THE FIGURE OF THE EARTH. By Frank C. 
Roberts, C. E. 

-HEALTHY FOUNDATIONS FOR HOUSES. By 
Glenn Brown. 

-WATER METERS : Comparative Tests of Accuracy. 
Delivery, etc. Distinctive Features of the Worth- 
ington, Kennedy, Siemens and Hesse Meters. By 
Ross E. Browne. 

-THE PRESERVATION OF TIMBER, by the use 
of Antiseptics By Samuel Bagster Boulton, C.E. 

—MECHANICAL INTEGRATORS. By Prof. Henry 

. S. H.Shaw, C. E. 

-FLOW OF WATER IN OPEN CHANNELS, PIPES, 
CONDUITS, SEWERS, &c. ; with Tables. By 
P. J. Flynn, C. E. 

-THE LUMINIFEROUS .ETHER. By Prof. De Vol- 
son Wood . 

—HANDBOOK OF MINERALOGY; Determination 
and Description of Minerals found in the United 
States. By Prof. J. C. Foye. 

-TREATISE ON THE THEORY OF THE CON- 
STRUCTION OF HELICOIDAL OBLIQUE 
ARCHES . By John L. Culley, C. E. 

-BEAMS AND GIRDERS. Practical Formulas for 
their Resistance. By P. H. Philbrick. 

—MODERN GUN COTTON : Its Manufacture, Prop- 
erties and Analysis By Lt. John P Wisser, U.S. A. 

—ROTARY MOTION; as Applied to the Gyroscope. 
By Gen. J G. Barnard. 

—LEVELING : Barometric, Trigonometric and Spirit. 
By Prof. I. O. Baker. 

-PETROLEUM : Its Production and Use. 

-SANITARY DRAINAGE of Buildings. 

-THE TREATMENT OF SEWAGE. By Tidy. 

-PLATE GIRDER CONSTRUCTION. By Hiroi. 



,'HE- 1 II 

028 156 570 9 

I.— ON TEu rarsiUAIi BASIS OF LIFE. I 
3 rci T. H. Huxley, LL.D. F.K.S. With an intrJ 
-on by a Professor in Yale College. 12mo, ppj 
*?aper Coders. Price 25 cents. 

II.— T20E CORRELATION OF VITAL 
?HYSICAL FORCES. By Prof. Geo roe F. Ba 
aF.D., of Y ale College. 36 pp. Paper Covers. Price I 

III.— AS REGARDS PROTOPLASM, in rell 
to Prof. Huxley's Physkal Basis of Life. B| 
3TJTCHisoNSTmLiNa,F.«,J.S. up. "% Z'lIoS&d 

IV.— ON THE HYPOTHESIS OF EVOL J) L 
Physical and Metaphysical. By Prof Ed~ai;1| 
3ope, 12mo., 72 pp. Paper Covers. Price H 

7.— SCIENTIFIC ADDRESSES:— 1. ':,i 1 
tUods and Tendencies ef Physical Inoesiigati n. 
Haze and Dust. 3. On the JSciet ific Che of Hie Jt 
nation. By Prof. John Tyndall, F.R.S. li 
pr.. Paper Covers. Price 25 ceni'j. Flex. Cluth t>u 

UO. VI.— NATURAL SELLOTION AS APPL| 
TO 1/AN By Alfred Ruf ell Wallace. 
pamphlet treats (i) c2 he Lwelopn^nt of Hn 
Races under the law of ^electit* -.; (2) tht,limitu oi 
ural Selection as applied to man. 54 pp. Price 9^ 

NO. VII -SPECTRUM A^ALYSI?. Tke 
Uirea by Pi^ Ak •'. Roscoe, Huggins, and Lockyer. 
ly illustrated. 83 pp Paper Covers. Price 25 cd 

NO, VIII.— T TE SUN. A sketch of the pre) 
atate of srienti-Se opini n as regards this body , ' 
account of the most recent discoveries and method 
ouserv tion. Bt Prof. C. A, Young, Ph.D , >i 
mcatb College. 38 pp Paper Covers. Price 25 cd 

NO. IX.- THE EARTH A OREAT MAGNETJ 
A. M. Mayer, Ph.D., of Stevens Institute. A 
profound! v murest-ng lecture on the subject of 
netistfi. 72 pp. Puper Covers. Price 25 cents. n 
Ible Cioth, 50 cento. 

*$ NO. X.— MYSTERIES OF THE VOICE 
EAR. By Prof. O. N. Rood, Columbia College, 
York. One of the most interesting lectures on r 
ever delivered. Original discoveries, brilliant ext| 
ments. Beautifully illu* 38 pp. Paper Covers 



